drm: Rip out the racy, unused vblank signal code.

Schedule a vblank signal, kill the process, and we'll go walking over freed
memory.  Given that no open-source userland exists using this, nor have I
ever heard of a consumer, just let this code die.

Signed-off-by: Eric Anholt <eric@anholt.net>
Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/drm/drm.h b/include/drm/drm.h
index 32e5096..8e77357 100644
--- a/include/drm/drm.h
+++ b/include/drm/drm.h
@@ -458,7 +458,7 @@
 	_DRM_VBLANK_FLIP = 0x8000000,   /**< Scheduled buffer swap should flip */
 	_DRM_VBLANK_NEXTONMISS = 0x10000000,	/**< If missed, wait for next vblank */
 	_DRM_VBLANK_SECONDARY = 0x20000000,	/**< Secondary display controller */
-	_DRM_VBLANK_SIGNAL = 0x40000000	/**< Send signal instead of blocking */
+	_DRM_VBLANK_SIGNAL = 0x40000000	/**< Send signal instead of blocking, unsupported */
 };
 
 #define _DRM_VBLANK_TYPES_MASK (_DRM_VBLANK_ABSOLUTE | _DRM_VBLANK_RELATIVE)