crush: drop unnecessary include from mapper.c

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/crush/mapper.c

@@ -20,7 +20,6 @@
 
 #include <linux/crush/crush.h>
 #include <linux/crush/hash.h>
-#include <linux/crush/mapper.h>
 
 /*
  * Implement the core CRUSH mapping algorithm.