Replace make_cleanup_restore_current_traceframe with RAII class

Replace make_cleanup_restore_current_traceframe with RAII class

I put the constructor in tracepoint.c because it needs to read
traceframe_number, and I prefer to do that than to expose
traceframe_number.

gdb/ChangeLog:

	* tracepoint.c (struct current_traceframe_cleanup): Remove.
	(do_restore_current_traceframe_cleanup): Remove.
	(restore_current_traceframe_cleanup_dtor): Remove.
	(make_cleanup_restore_current_traceframe): Remove.
	(scoped_restore_current_traceframe::scoped_restore_current_traceframe):
	New.
	* tracepoint.h (struct scoped_restore_current_traceframe): New.
	* infrun.c (fetch_inferior_event): Use
	scoped_restore_current_traceframe.