Replace clear_hook_in_cleanup with scoped_restore_hook_in

Replace clear_hook_in_cleanup with scoped_restore_hook_in

This removes clear_hook_in_cleanup in favor of a scoped_restore-like
class.  scoped_restore itself can't be used because hook_in is a
bitfield.

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

	* cli/cli-script.c (class scoped_restore_hook_in): New.
	(clear_hook_in_cleanup): Remove.
	(execute_cmd_pre_hook, execute_cmd_post_hook): Use
	scoped_restore_hook_in.