remove useless check of `m` in arrangelayers()

it is supossed to avoid a crash when we pass m=NULL as argument
however it would crash anyway and also because we should not pass m=NULL

dwl.c

@@ -596,8 +596,6 @@ arrangelayers(Monitor *m)
 		ZWLR_LAYER_SHELL_V1_LAYER_TOP,
 	};
 	LayerSurface *layersurface;
-	if (!m || !m->wlr_output->enabled)
-		return;
 
 	/* Arrange exclusive surfaces from top->bottom */
 	for (i = 3; i >= 0; i--)