drm: remove the list_head from drm_mode_set

It's unused. At it confused me quite a bit until I've discovered that.

Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_crtc.h

@@ -676,8 +676,6 @@ struct drm_plane {
  * This is used to set modes.
  */
 struct drm_mode_set {
-	struct list_head head;
-
 	struct drm_framebuffer *fb;
 	struct drm_crtc *crtc;
 	struct drm_display_mode *mode;