fix (breville?airrounderplus_heater): hide heat_mode from the user

This should be internal (the dp is still accessible from diagnostics).

Issue #3582

custom_components/tuya_local/devices/breville_airrounderplus_heater.yaml

@@ -35,6 +35,7 @@ entities:
       - id: 4
         type: string
         name: heat_mode
+        hidden: true
         mapping:
           - dps_val: heat_mid
             value: low