docs(kicker): remove unsupported PUBLISH_ON_PROD

kicker.json

@@ -64,12 +64,6 @@
       "name": "DOCKER_PUBLISH_ARGS",
       "description": "Additional [`skopeo copy` arguments](https://github.com/containers/skopeo/blob/master/docs/skopeo-copy.1.md#options)"
     },
-    {
-      "name": "PUBLISH_ON_PROD",
-      "description": "Determines whether this job is enabled on `master` branch",
-      "default": "true",
-      "type": "boolean"
-    },
     {
       "name": "DOCKER_PROD_PUBLISH_STRATEGY",
       "description": "Defines the publish to production strategy.",