config: remove unneeded option

config.js

     // a call is hangup.
     // enableClosePage: false,
 
-    // Enabling pre join page will add an additional step before starting the meeting,
-    // where the user can configure its devices and choose the way he
-    // joins audio (by phone/or web).
-    // prejoinPageEnabled: false,
-
     // Disable hiding of remote thumbnails when in a 1-on-1 conference call.
     // disable1On1Mode: false,
 

react/features/toolbox/components/web/Toolbox.js

     setOverflowMenuVisible,
     setToolbarHovered
 } from '../../actions';
-import AudioMuteButton from '../AudioMuteButton';
 import AudioSettingsButton from './AudioSettingsButton';
 import DownloadButton from '../DownloadButton';
 import { isToolboxVisible } from '../../functions';
 import OverflowMenuProfileItem from './OverflowMenuProfileItem';
 import MuteEveryoneButton from './MuteEveryoneButton';
 import ToolbarButton from './ToolbarButton';
-import VideoMuteButton from '../VideoMuteButton';
 import VideoSettingsButton from './VideoSettingsButton';
 import {
     ClosedCaptionButton
      */
     _fullScreen: boolean,
 
-    /**
-     * Whether or not the prejoin page is enabled.
-     */
-    _prejoinPageEnabled: boolean,
-
     /**
      * Whether or not the tile view is enabled.
      */
      */
     _renderAudioButton() {
         return this._shouldShowButton('microphone')
-            ? this.props._prejoinPageEnabled
-                ? <AudioSettingsButton
-                    key = 'asb'
-                    visible = { true } />
-                : <AudioMuteButton
-                    key = 'amb'
-                    visible = { true } />
+            ? <AudioSettingsButton
+                key = 'asb'
+                visible = { true } />
             : null;
     }
 
      */
     _renderVideoButton() {
         return this._shouldShowButton('camera')
-            ? this.props._prejoinPageEnabled
-                ? <VideoSettingsButton
-                    key = 'vsb'
-                    visible = { true } />
-                : <VideoMuteButton
-                    key = 'vmb'
-                    visible = { true } />
+            ? <VideoSettingsButton
+                key = 'vsb'
+                visible = { true } />
             : null;
     }
 
     const {
         callStatsID,
         enableFeaturesBasedOnToken,
-        iAmRecorder,
-        prejoinPageEnabled
+        iAmRecorder
     } = state['features/base/config'];
     const sharedVideoStatus = state['features/shared-video'].status;
     const {
         _localParticipantID: localParticipant.id,
         _localRecState: localRecordingStates,
         _overflowMenuVisible: overflowMenuVisible,
-        _prejoinPageEnabled: prejoinPageEnabled,
         _raisedHand: localParticipant.raisedHand,
         _screensharing: localVideo && localVideo.videoType === 'desktop',
         _sharingVideo: sharedVideoStatus === 'playing'