cleanup: Remove unused code.

react/features/base/conference/actionTypes.js

  */
 export const SET_ROOM = 'SET_ROOM';
 
-/**
- * The type of (redux) action, which indicates if a SIP gateway is enabled on
- * the server.
- *
- * {
- *     type: SET_SIP_GATEWAY_ENABLED
- *     isSIPGatewayEnabled: boolean
- * }
- */
-export const SET_SIP_GATEWAY_ENABLED = 'SET_SIP_GATEWAY_ENABLED';
-
 /**
  * The type of (redux) action which updates the current known status of the
  * moderator features for starting participants as audio or video muted.

react/features/base/conference/reducer.js

     SET_PASSWORD,
     SET_PENDING_SUBJECT_CHANGE,
     SET_ROOM,
-    SET_SIP_GATEWAY_ENABLED,
     SET_START_MUTED_POLICY
 } from './actionTypes';
 import { isRoomValid } from './functions';
         case SET_ROOM:
             return _setRoom(state, action);
 
-        case SET_SIP_GATEWAY_ENABLED:
-            return _setSIPGatewayEnabled(state, action);
-
         case SET_START_MUTED_POLICY:
             return {
                 ...state,
     });
 }
 
-/**
- * Reduces a specific Redux action SET_SIP_GATEWAY_ENABLED of the feature
- * base/conference.
- *
- * @param {Object} state - The Redux state of the feature base/conference.
- * @param {Action} action - The Redux action SET_SIP_GATEWAY_ENABLED to reduce.
- * @private
- * @returns {Object} The new state of the feature base/conference after the
- * reduction of the specified action.
- */
-function _setSIPGatewayEnabled(state, action) {
-    return set(state, 'isSIPGatewayEnabled', action.isSIPGatewayEnabled);
-}