module: remove rmmod --wait option.

The option to wait for a module reference count to reach zero was in
the initial module implementation, but it was never supported in
modprobe (you had to use rmmod --wait).  After discussion with Lucas,
It has been deprecated (with a 10 second sleep) in kmod for the last
year.

This finally removes it: the flag will evoke a printk warning and a
normal (non-blocking) remove attempt.

Cc: Lucas De Marchi <lucas.de.marchi@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/module.h

@@ -367,9 +367,6 @@ struct module
 	/* What modules do I depend on? */
 	struct list_head target_list;
 
-	/* Who is waiting for us to be unloaded */
-	struct task_struct *waiter;
-
 	/* Destruction function. */
 	void (*exit)(void);