call tree_render() only after commands which require it

Saves one call of tree_render for exec, for example

src/handlers.c

@@ -106,7 +106,6 @@ static int handle_key_press(xcb_key_press_event_t *event) {
     }
 
     parse_cmd(bind->command);
-    tree_render();
     return 1;
 }