Remove additional self from update function in RainMachine (#18810)

homeassistant/components/sensor/rainmachine.py

@@ -77,7 +77,7 @@ class RainMachineSensor(RainMachineEntity):
     async def async_added_to_hass(self):
         """Register callbacks."""
         @callback
-        def update(self):
+        def update():
             """Update the state."""
             self.async_schedule_update_ha_state(True)