Fixes #535 send mode info on DRM refresh once

When DRM refreshed, wlr_output_set_mode is called. It would then call
the DRM set_mode callback which sends the updated matrix and mode info.

However once that call completed it would then immediantly send the
information again. This is handled poorly by xwayland, causing it to
scale up the clients twice.

types/wlr_output.c

@@ -163,16 +163,7 @@ bool wlr_output_set_mode(struct wlr_output *output,
 	if (!output->impl || !output->impl->set_mode) {
 		return false;
 	}
-	bool result = output->impl->set_mode(output, mode);
-	if (result) {
-		wlr_output_update_matrix(output);
-
-		struct wl_resource *resource;
-		wl_resource_for_each(resource, &output->wl_resources) {
-			wlr_output_send_current_mode_to_resource(resource);
-		}
-	}
-	return result;
+	return output->impl->set_mode(output, mode);
 }
 
 bool wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,