Remove make_cleanup_regcache_xfree

Remove make_cleanup_regcache_xfree

This removes make_cleanup_regcache_xfree in favor of using
std::unique_ptr as the return type of frame_save_as_regcache.

gdb/ChangeLog
2017-09-25  Tom Tromey  <tom@tromey.com>

	* spu-tdep.c (spu2ppu_sniffer): Update.
	* regcache.h (make_cleanup_regcache_xfree): Don't declare.
	* regcache.c (do_regcache_xfree, make_cleanup_regcache_xfree):
	Remove.
	* ppc-linux-tdep.c (ppu2spu_sniffer): Update.
	* mi/mi-main.c (mi_cmd_data_list_changed_registers): Update.
	* frame.h (frame_save_as_regcache): Return std::unique_ptr.
	* frame.c (frame_save_as_regcache): Return std::unique_ptr.
	(frame_pop): Update.