slab: remove duplicate kmem_cache_init_late() declarations

kmem_cache_init_late() has been declared in slab.h

CC: Nick Piggin <npiggin@suse.de>
CC: Matt Mackall <mpm@selenic.com>
CC: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slob.c

@@ -692,3 +692,8 @@ void __init kmem_cache_init(void)
 {
 	slob_ready = 1;
 }
+
+void __init kmem_cache_init_late(void)
+{
+	/* Nothing to do */
+}