Garbage collect dummy_frame_ctx_saver

Garbage collect dummy_frame_ctx_saver

Since the "finish" command and infcall's FSMs are now responsible for
saving the return value, the dummy_frame_ctx_saver is no longer needed
anywhere.

gdb/ChangeLog:
2015-09-09  Pedro Alves  <palves@redhat.com>

	* infcall.c (struct dummy_frame_context_saver): Delete.
	(dummy_frame_context_saver_free, dummy_frame_context_saver_dtor)
	(dummy_frame_context_saver_drop)
	(dummy_frame_context_saver_cleanup)
	(dummy_frame_context_saver_get_regs)
	(dummy_frame_context_saver_setup): Delete.
	* infcall.h (dummy_frame_context_saver_drop)
	(dummy_frame_context_saver_cleanup)
	(dummy_frame_context_saver_get_regs, dummy_frame_context_saver):
	Delete.
	(get_return_value): Remove 'ctx_saver' paremeter.  Adjust.
	* inferior.h (get_return_value): Remove 'ctx_saver' paremeter.
	* python/py-finishbreakpoint.c (bpfinishpy_pre_stop_hook): Adjust.