Use TRY/CATCH in remove_prev_frame

Use TRY/CATCH in remove_prev_frame

This changes remove_prev_frame to use TRY/CATCH instead of a cleanup.
TRY/CATCH seemed appropriate here because the cleanup is only needed
in the case where an exception is thrown.

Tested by the buildbot.

ChangeLog
2018-05-25  Tom Tromey  <tom@tromey.com>

	* frame.c (remove_prev_frame): Remove.
	(get_prev_frame_if_no_cycle): Use TRY/CATCH.