Goldair GPCV heater: remove old timer attribute

This was originally left so as not to upset any existing use, but the
timer entity has been available since 2022 so it is long since time to
clean it up.

custom_components/tuya_local/devices/goldair_gpcv_heater.yaml

@@ -22,9 +22,6 @@ entities:
       - id: 4
         type: integer
         name: current_temperature
-      - id: 5
-        type: integer
-        name: timer
       - id: 7
         type: string
         mapping: