inliner: Remove unused transform_lang_insert_block hook

This struct copy_body_data's hook is always NULL since merge
of the tuples branch, before that it has been shortly used by the C++
FE during ctor/dtor cloning to chain the remapped blocks, but only
very shortly, before transform_lang_insert_block was a bool and
the call to insert_block was done through a langhook.
I'd say that for something that hasn't been used since 4.4 there is
zero chance we'll want to use it again in the near future.

2021-11-23  Jakub Jelinek  <jakub@redhat.com>

gcc/
	* tree-inline.h (struct copy_body_data): Remove
	transform_lang_insert_block member.
	* tree-inline.c (remap_block): Don't call
	id->transform_lang_insert_block.
	(optimize_inline_calls, copy_gimple_seq_and_replace_locals,
	tree_function_versioning, maybe_inline_call_in_expr,
	copy_fn): Don't initialize id.transform_lang_insert_block.
	* gimplify.c (gimplify_omp_loop): Likewise.
gcc/c/
	* c-typeck.c (c_clone_omp_udr): Don't initialize
	id.transform_lang_insert_block.
gcc/cp/
	* semantics.c (clone_omp_udr): Don't initialize
	id.transform_lang_insert_block.
	* optimize.c (clone_body): Likewise.