libstdc++: Remove test dependencies on _GLIBCXX_USE_C99_STDINT_TR1

These #ifdef checks should have been removed in r9-2029-g612c9c702e2c9e
when the u16string_view and u32string_view aliases were changed to be
defined unconditionally.

libstdc++-v3/ChangeLog:

	* testsuite/21_strings/basic_string_view/typedefs.cc: Remove
	dependency on _GLIBCXX_USE_C99_STDINT_TR1.
	* testsuite/experimental/string_view/typedefs.cc: Likewise.