vect: Remove vec_outside/inside_cost fields

vect: Remove vec_outside/inside_cost fields

The vector costs now use a common base class instead of being
completely abstract.  This means that there's no longer a
need to record the inside and outside costs separately.

gcc/
	* tree-vectorizer.h (_loop_vec_info): Remove vec_outside_cost
	and vec_inside_cost.
	(vector_costs::outside_cost): New function.
	* tree-vect-loop.c (_loop_vec_info::_loop_vec_info): Update
	after above.
	(vect_estimate_min_profitable_iters): Likewise.
	(vect_better_loop_vinfo_p): Get the inside and outside costs
	from the loop_vec_infos' vector_costs.