Remove for_each_inferior

Remove for_each_inferior

This patch removes for_each_inferior, replacing all its usages with
for_each_thread.

gdb/gdbserver/ChangeLog:

	* inferiors.c (for_each_inferior): Remove.
	(clear_inferiors): Use for_each_thread.
	* inferiors.h (for_each_inferior): Remove.
	* linux-low.c (linux_wait_for_event_filtered): Use
	for_each_thread.
	(linux_stabilize_threads): Likewise.
	* regcache.c (regcache_release): Likewise.
	* server.c (gdb_wants_all_threads_stopped): Likewise.
	(clear_pending_status_callback): Remove.
	(handle_status): Use for_each_thread.
	(captured_main): Likewise.
	* win32-low.c (child_init_thread_list): Likewise.
	(win32_clear_inferiors): Likewise.
	(fake_breakpoint_event): Likewise.