PHW218: remove scale from ORP

Issue #580

custom_components/tuya_local/devices/phw218_waterquality_monitor.yaml

@@ -36,8 +36,6 @@ secondary_entities:
         name: sensor
         class: measurement
         unit: mV
-        mapping:
-          - scale: 10
   - entity: sensor
     name: Electrical conductivity
     icon: "mdi:omega"