locking: Remove unused prototype

commit 910067d1(remove generic__raw_read_trylock()) removed the
implementation but left the prototype around. Remove it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/spinlock.h

@@ -79,8 +79,6 @@
  */
 #include <linux/spinlock_types.h>
 
-extern int __lockfunc generic__raw_read_trylock(raw_rwlock_t *lock);
-
 /*
  * Pull the __raw*() functions/declarations (UP-nondebug doesnt need them):
  */