ref(toolbar): removed unused dialpad logic

The old toolbar had a dialpad button that did a no-op.
Remove the remnant of that logic.

conference.js

             }
         });
 
-        room.on(
-            JitsiConferenceEvents.DTMF_SUPPORT_CHANGED,
-            isDTMFSupported => {
-                APP.UI.updateDTMFSupport(isDTMFSupported);
-            }
-        );
-
         APP.UI.addListener(UIEvents.AUDIO_MUTED, muted => {
             this.muteAudio(muted);
         });

lang/main.json

         "hangup": "Leave",
         "login": "Login",
         "logout": "Logout",
-        "dialpad": "Open / Close dialpad",
         "sharedVideoMutedPopup": "Your shared video has been muted so that you can talk to the other members.",
         "micMutedPopup": "Your microphone has been muted so that you would fully enjoy your shared video.",
         "talkWhileMutedPopup": "Trying to speak? You are muted.",

modules/UI/UI.js

     Chat.updateChatConversation(from, displayName, message, stamp);
 };
 
-// TODO: With Toolbox v2 this got scrapped. Remove?
-// eslint-disable-next-line no-empty-function
-UI.updateDTMFSupport = () => { };
-
 UI.updateRecordingState = function(state) {
     Recording.updateRecordingState(state);
 };