Remove load interleaving code

Remove load interleaving code

The following removes the non-SLP load interleaving code which was
almost unused.

	* tree-vectorizer.h (vect_transform_grouped_load): Remove.
	(vect_record_grouped_load_vectors): Likewise.
	* tree-vect-data-refs.cc (vect_permute_load_chain): Likewise.
	(vect_shift_permute_load_chain): Likewise.
	(vect_transform_grouped_load): Likewise.
	(vect_record_grouped_load_vectors): Likewise.
	* tree-vect-stmts.cc (vectorizable_load): Remove comments
	about load interleaving.