Change setup_breakpoint_reporting to return a scoped_restore

Change setup_breakpoint_reporting to return a scoped_restore

This changes setup_breakpoint_reporting to return a scoped_restore,
allowing for some cleanup removal.

ChangeLog
2017-09-11  Tom Tromey  <tom@tromey.com>

	* mi/mi-cmd-catch.c (mi_cmd_catch_assert)
	(mi_cmd_catch_exception, mi_catch_load_unload): Update.
	* mi/mi-cmd-break.c (setup_breakpoint_reporting): Return a
	scoped_restore.
	(mi_cmd_break_insert_1): Update.
	* mi/mi-cmd-break.h (setup_breakpoint_reporting): Return a
	scoped_restore.