Remove find_inferior_id

Remove find_inferior_id

Remove find_inferior_id, replacing its usages with find_thread_ptid.
find_thread_ptid was implemented using find_inferior_id, so move the
implementation there instead.

gdb/gdbserver/ChangeLog:

	* inferiors.c (find_inferior_id): Remove.
	(find_thread_ptid): Move implemention from find_inferior_id to
	here.
	* inferiors.h (find_inferior_id): Remove.
	* server.c (handle_status): Use find_thread_ptid.
	(process_serial_event): Likewise.
	* thread-db.c (find_one_thread): Likewise.
	(thread_db_thread_handle): Likewise.
	* win32-low.c (thread_rec): Likewise.
	(child_delete_thread): Likewise.
	(win32_thread_alive): Likewise.
	(get_child_debug_event): Likewise.