exofs: Remove superfluous dependency on buffer_head and writeback

exofs_releasepage && exofs_invalidatepage are never called.
Leave the WARN_ONs but remove any code. Remove the

cleanup other stale #includes.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

fs/exofs/super.c

@@ -31,7 +31,6 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#include <linux/smp_lock.h>
 #include <linux/string.h>
 #include <linux/parser.h>
 #include <linux/vfs.h>