chore: remove deprecated api /superset/available_domains (#24381)

UPDATING.md

@@ -34,6 +34,7 @@ assists people when migrating to a new version.
 
 ### Breaking Changes
 
+- [24381](https://github.com/apache/superset/pull/24381): Removed deprecated API `/superset/available_domains/`
 - [24359](https://github.com/apache/superset/pull/24359): Removed deprecated APIs `/superset/estimate_query_cost/..`, `/superset/results/..`, `/superset/sql_json/..`, `/superset/csv/..`
 - [24345](https://github.com/apache/superset/pull/24345) Converts `ENABLE_BROAD_ACTIVITY_ACCESS` and `MENU_HIDE_USER_INFO` into feature flags and changes the value of `ENABLE_BROAD_ACTIVITY_ACCESS` to `False` as it's more secure.
 - [24342](https://github.com/apache/superset/pull/24342): Removed deprecated API `/superset/tables/<int:db_id>/<schema>/...`

superset/views/core.py

@@ -1100,21 +1100,6 @@ def recent_activity(self, user_id: int) -> FlaskResponse:
 
         return json_success(json.dumps(payload, default=utils.json_int_dttm_ser))
 
-    @api
-    @has_access_api
-    @event_logger.log_this
-    @expose("/available_domains/", methods=("GET",))
-    @deprecated(new_target="/api/v1/available_domains/")
-    def available_domains(self) -> FlaskResponse:  # pylint: disable=no-self-use
-        """
-        Returns the list of available Superset Webserver domains (if any)
-        defined in config. This enables charts embedded in other apps to
-        leverage domain sharding if appropriately configured.
-        """
-        return Response(
-            json.dumps(conf.get("SUPERSET_WEBSERVER_DOMAINS")), mimetype="text/json"
-        )
-
     @api
     @has_access_api
     @event_logger.log_this