Remove usage of find_inferior in resume

Remove usage of find_inferior in resume

Change find_inferior with find_thread.  Since we can now pass arguments
directly instead of through a void pointer, we don't need the
visit_actioned_threads_data structure anymore.

gdb/gdbserver/ChangeLog:

	* server.c (struct visit_actioned_threads_data): Remove.
	(visit_actioned_threads): Change prototype to take arguments
	directly.
	(resume): Use find_thread instead of find_inferior.