Remove flush from render methods

This causes flickering because the render is done prematurely.

src/ui/tray.rs

@@ -95,7 +95,6 @@ impl widget::Widget for Tray {
                 (xcb::CONFIG_WINDOW_X as u16, xpos)
             ]);
         }
-        self.conn.flush();
     }
 
     fn handle_event(&mut self, event: &xcb::GenericEvent, is_finishing: bool) -> bool {