Improve description of `mode` field in `geniushub.set_zone_mode` action (#139513)

Improve description of `mode` field in 'geniushub.set_zone_mode' action

As the three choices for the `mode` field show up as radio buttons in the UI the description does not need to repeat them.

This improves translations by avoiding any over-translation of these values.

homeassistant/components/geniushub/strings.json

@@ -45,7 +45,7 @@
         },
         "mode": {
           "name": "[%key:common::config_flow::data::mode%]",
-          "description": "One of: off, timer or footprint."
+          "description": "The zone's operating mode."
         }
       }
     },