Remove cleanup from infrun.c

Remove cleanup from infrun.c

This removes a cleanup from infrun.c by taking advantage of the
previous patch to introduce a use of unique_xmalloc_ptr.

gdb/ChangeLog
2018-09-17  Tom Tromey  <tom@tromey.com>

	* infrun.c (struct infcall_suspend_state) <registers>: Now a
	unique_ptr.
	<siginfo_data>: Now a unique_xmalloc_ptr.
	(save_infcall_suspend_state, restore_infcall_suspend_state)
	(discard_infcall_suspend_state)
	(get_infcall_suspend_state_regcache): Update.