Nothing now uses the grouped_store value passed back by
vect_transform_stmt, so we might as well remove it.

2018-08-01  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vect_transform_stmt): Remove grouped_store
	argument.
	* tree-vect-stmts.c (vect_transform_stmt): Likewise.
	* tree-vect-loop.c (vect_transform_loop_stmt): Update call accordingly.
	(vect_transform_loop): Likewise.
	* tree-vect-slp.c (vect_schedule_slp_instance): Likewise.

From-SVN: r263216