config: remove obsolete options

config.js

     // bridge itself is reachable via UDP)
     // useTurnUdp: false
 
-    // Enable IPv6 support.
-    // useIPv6: true,
-
     // Enables / disables a data communication channel with the Videobridge.
     // Values can be 'datachannel', 'websocket', true (treat it as
     // 'datachannel'), undefined (treat it as 'datachannel') and false (don't
     // UI
     //
 
-    // Use display name as XMPP nickname.
-    // useNicks: false,
-
     // Require users to always specify a display name.
     // requireDisplayName: true,
 

react/features/base/config/configWhitelist.js

     'stereo',
     'subject',
     'testing',
-    'useIPv6',
-    'useNicks',
     'useStunTurn',
     'useTurnUdp',
     'webrtcIceTcpDisable',