sched/wait: Remove unused bit_wait_io_timeout

bit_wait_io_timeout has been unused since 2016's
commit 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit")

Remove it.

Signed-off-by: "Dr. David Alan Gilbert" <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Reviewed-by: Tim Chen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

include/linux/wait_bit.h

···
 extern int bit_wait(struct wait_bit_key *key, int mode);
 extern int bit_wait_io(struct wait_bit_key *key, int mode);
 extern int bit_wait_timeout(struct wait_bit_key *key, int mode);
-extern int bit_wait_io_timeout(struct wait_bit_key *key, int mode);
 
 /**
  * wait_on_bit - wait for a bit to be cleared

kernel/sched/wait_bit.c

···
 }
 EXPORT_SYMBOL_GPL(bit_wait_timeout);
 
-__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
-{
-	unsigned long now = READ_ONCE(jiffies);
-
-	if (time_after_eq(now, word->timeout))
-		return -EAGAIN;
-	io_schedule_timeout(word->timeout - now);
-	if (signal_pending_state(mode, current))
-		return -EINTR;
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
-
 void __init wait_bit_init(void)
 {
 	int i;