drm/mm: Remove MM_UNUSED_TARGET

This was missed in

commit c700c67b
Author: David Herrmann <dh.herrmann@gmail.com>
Date:   Sat Jul 27 13:39:28 2013 +0200

    drm/mm: remove unused API

Cc: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_mm.c

@@ -47,8 +47,6 @@
 #include <linux/seq_file.h>
 #include <linux/export.h>
 
-#define MM_UNUSED_TARGET 4
-
 static struct drm_mm_node *drm_mm_search_free_generic(const struct drm_mm *mm,
 						unsigned long size,
 						unsigned alignment,