Remove dead code dealing with non-SLP

Remove dead code dealing with non-SLP

After vect_analyze_loop_operations is gone we can clean up
vect_analyze_stmt as it is no longer called out of SLP context.

	* tree-vectorizer.h (vect_analyze_stmt): Remove stmt-info
	and need_to_vectorize arguments.
	* tree-vect-slp.cc (vect_slp_analyze_node_operations_1):
	Adjust.
	* tree-vect-stmts.cc (can_vectorize_live_stmts): Remove
	stmt_info argument and remove non-SLP path.
	(vect_analyze_stmt): Remove stmt_info and need_to_vectorize
	argument and prune paths no longer reachable.
	(vect_transform_stmt): Adjust.