libstdc++: Remove dg-options "-std=gnu++20" from 23_containers tests

The testsuite will automatically select C++20 for these tests now, and
removing the hardcoded -std option allows them to be tested for C++23
and C++26 as well.

libstdc++-v3/ChangeLog:

	* testsuite/23_containers/array/comparison_operators/96851.cc:
	Remove dg-options -std=gnu++2a.
	* testsuite/23_containers/array/comparison_operators/constexpr.cc:
	Likewise.
	* testsuite/23_containers/array/creation/1.cc: Likewise.
	* testsuite/23_containers/array/creation/110167.cc: Likewise.
	* testsuite/23_containers/array/creation/2.cc: Likewise.
	* testsuite/23_containers/array/creation/3_neg.cc: Likewise.
	* testsuite/23_containers/array/requirements/constexpr_fill.cc:
	Likewise.
	* testsuite/23_containers/array/requirements/constexpr_swap.cc:
	Likewise.
	* testsuite/23_containers/deque/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/deque/erasure.cc: Likewise.
	* testsuite/23_containers/deque/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/deque/operators/cmp_c++20.cc:
	Likewise.
	* testsuite/23_containers/forward_list/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/forward_list/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/forward_list/erasure.cc: Likewise.
	* testsuite/23_containers/forward_list/modifiers/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/forward_list/operations/remove_cxx20_return.cc:
	Likewise.
	* testsuite/23_containers/forward_list/operations/unique_cxx20_return.cc:
	Likewise.
	* testsuite/23_containers/list/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/list/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/list/erasure.cc: Likewise.
	* testsuite/23_containers/list/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/list/operations/remove_cxx20_return.cc:
	Likewise.
	* testsuite/23_containers/list/operations/unique_cxx20_return.cc:
	Likewise.
	* testsuite/23_containers/map/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/map/erasure.cc: Likewise.
	* testsuite/23_containers/map/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/map/operations/contains.cc: Likewise.
	* testsuite/23_containers/map/operators/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/multimap/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/multimap/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/multimap/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/multimap/operators/cmp_c++20.cc:
	Likewise.
	* testsuite/23_containers/multiset/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/multiset/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/multiset/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/multiset/operators/cmp_c++20.cc:
	Likewise.
	* testsuite/23_containers/priority_queue/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/queue/92878_92947.cc: Likewise.
	* testsuite/23_containers/queue/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/set/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/set/erasure.cc: Likewise.
	* testsuite/23_containers/set/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/set/operations/contains.cc: Likewise.
	* testsuite/23_containers/set/operators/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/span/1.cc: Likewise.
	* testsuite/23_containers/span/101411.cc: Likewise.
	* testsuite/23_containers/span/2.cc: Likewise.
	* testsuite/23_containers/span/deduction.cc: Likewise.
	* testsuite/23_containers/span/explicit.cc: Likewise.
	* testsuite/23_containers/span/layout_compat.cc: Likewise.
	* testsuite/23_containers/span/lwg3255.cc: Likewise.
	* testsuite/23_containers/span/nothrow_cons.cc: Likewise.
	* testsuite/23_containers/span/trivially_copyable.cc: Likewise.
	* testsuite/23_containers/stack/92878_92947.cc: Likewise.
	* testsuite/23_containers/stack/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/unordered_map/48101-3_neg.cc:
	Likewise.
	* testsuite/23_containers/unordered_map/erasure.cc: Likewise.
	* testsuite/23_containers/unordered_map/modifiers/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/unordered_map/operations/1.cc:
	Likewise.
	* testsuite/23_containers/unordered_map/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/unordered_multimap/48101-3_neg.cc:
	Likewise.
	* testsuite/23_containers/unordered_multimap/modifiers/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/unordered_multimap/operations/1.cc:
	Likewise.
	* testsuite/23_containers/unordered_multimap/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/unordered_multiset/48101-3_neg.cc:
	Likewise.
	* testsuite/23_containers/unordered_multiset/modifiers/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/unordered_multiset/operations/1.cc:
	Likewise.
	* testsuite/23_containers/unordered_multiset/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/unordered_set/48101-3_neg.cc:
	Likewise.
	* testsuite/23_containers/unordered_set/erasure.cc: Likewise.
	* testsuite/23_containers/unordered_set/modifiers/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/unordered_set/operations/1.cc:
	Likewise.
	* testsuite/23_containers/unordered_set/operations/contains.cc:
	Likewise.
	* testsuite/23_containers/vector/48101-3_neg.cc: Likewise.
	* testsuite/23_containers/vector/bool/capacity/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/vector/bool/cons/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/element_access/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/iterator_c++20.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/modifiers/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/capacity/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/cmp_c++20.cc: Likewise.
	* testsuite/23_containers/vector/cons/constexpr.cc: Likewise.
	* testsuite/23_containers/vector/data_access/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/element_access/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/erasure.cc: Likewise.
	* testsuite/23_containers/vector/modifiers/assign/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/modifiers/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/modifiers/emplace/92878_92947.cc:
	Likewise.
	* testsuite/23_containers/vector/modifiers/swap/constexpr.cc:
	Likewise.
	* testsuite/23_containers/vector/requirements/version.cc:
	Likewise.