Revert "drm/gem: Warn on illegal use of the dumb buffer interface v2"

This reverts commit 355a701838.

This had some bad side effects under normal operation, and should
have been dropped earlier.

Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_gem.h

@@ -119,13 +119,6 @@ struct drm_gem_object {
 	 * simply leave it as NULL.
 	 */
 	struct dma_buf_attachment *import_attach;
-
-	/**
-	 * dumb - created as dumb buffer
-	 * Whether the gem object was created using the dumb buffer interface
-	 * as such it may not be used for GPU rendering.
-	 */
-	bool dumb;
 };
 
 void drm_gem_object_release(struct drm_gem_object *obj);