compositor-drm: remove a stale comment

This comment became stale in:

commit 65a11e1039
Author: Kristian Høgsberg <krh@bitplanet.net>
Date:   Fri Aug 3 11:30:18 2012 -0400

    compositor: Accumulate damage per plane

Now it is just misleading. Remove it.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

src/compositor-drm.c

@@ -564,11 +564,6 @@ drm_disable_unused_sprites(struct weston_output *output_base)
 	}
 }
 
-/*
- * This function must take care to damage any previously assigned surface
- * if the sprite ends up binding to a different surface than in the
- * previous frame.
- */
 static struct weston_plane *
 drm_output_prepare_overlay_surface(struct weston_output *output_base,
 				   struct weston_surface *es)