sh64: Remove long unused mid_sched macro

interruptible_sleep_on() is referenced for use in the mid_sched macro
which is not used anywhere.  Remove reference and macro as well as the
comment which appears to belong with them.
Signed-off-by: Andreas Bombe <aeb@debian.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/process_64.c

@@ -504,13 +504,6 @@ out:
 	return error;
 }
 
-/*
- * These bracket the sleeping functions..
- */
-extern void interruptible_sleep_on(wait_queue_head_t *q);
-
-#define mid_sched	((unsigned long) interruptible_sleep_on)
-
 #ifdef CONFIG_FRAME_POINTER
 static int in_sh64_switch_to(unsigned long pc)
 {