fix(chat) stop using nicknames

We stopped providing a way to set them, so don't render them either.

Also cleanup some leftover config options.

config.js

      forceJVB121Ratio
      hiddenDomain
      ignoreStartMuted
-     nick
      startBitrate
      */
 

doc/example-config-files/config.js.example

         muc: 'conference.jitsi.example.com', // FIXME: use XEP-0030
         bridge: 'jitsi-videobridge.jitsi.example.com' // FIXME: use XEP-0030
     },
-    useNicks: false,
     bosh: '//jitsi.example.com/http-bind' // FIXME: use xep-0156 for that
 };

doc/example-config-files/multidomain/config.js.multidomain.example

         muc: 'conference.'+subdomain+'jitsi.example.com', // FIXME: use XEP-0030
         focus: 'focus.jitsi.example.com',
     },
-    useNicks: false,
     bosh: '//jitsi.example.com/http-bind', // FIXME: use xep-0156 for that
     websocket: 'wss://jitsi.example.com/xmpp-websocket'
 };

modules/UI/UI.js

     });
 };
 
-UI.askForNickname = function() {
-    // eslint-disable-next-line no-alert
-    return window.prompt('Your nickname (optional)');
-};
-
 /**
  * Sets muted audio state for participant
  */

react/features/base/config/configWhitelist.js

     'localRecording',
     'maxFullResolutionParticipants',
     'minParticipants',
-    'nick',
     'openBridgeChannel',
     'opusMaxAverageBitrate',
     'p2p',

react/features/chat/middleware.js

 
     conference.on(
         JitsiConferenceEvents.MESSAGE_RECEIVED,
-        (id, message, timestamp, nick) => {
+        (id, message, timestamp) => {
             _handleReceivedMessage(store, {
                 id,
                 message,
-                nick,
                 privateMessage: false,
                 timestamp
             });
                 id,
                 message,
                 privateMessage: true,
-                timestamp,
-                nick: undefined
+                timestamp
             });
         }
     );
  * @param {Object} message - The message object.
  * @returns {void}
  */
-function _handleReceivedMessage({ dispatch, getState }, { id, message, nick, privateMessage, timestamp }) {
+function _handleReceivedMessage({ dispatch, getState }, { id, message, privateMessage, timestamp }) {
     // Logic for all platforms:
     const state = getState();
     const { isOpen: isChatOpen } = state['features/chat'];
     // backfilled for a participant that has left the conference.
     const participant = getParticipantById(state, id) || {};
     const localParticipant = getLocalParticipant(getState);
-    const displayName = participant.name || nick || getParticipantDisplayName(state, id);
+    const displayName = getParticipantDisplayName(state, id);
     const hasRead = participant.local || isChatOpen;
-    const timestampToDate = timestamp
-        ? new Date(timestamp) : new Date();
+    const timestampToDate = timestamp ? new Date(timestamp) : new Date();
     const millisecondsTimestamp = timestampToDate.getTime();
 
     dispatch(addMessage({