Move roomnameGenerator.js out of features/base/util

Over time features/base/util became a bucket where people seemed to dump
just about anything they couldn't think of a better place for. That's a
trend I don't like encouraging. Given that roomnameGenerator.js is
currently used in features/welcome only, I'm fine with moving it there
for the greater good.

react/features/welcome/components/AbstractWelcomePage.js

@@ -4,7 +4,8 @@ import { appNavigate } from '../../app';
 import { isRoomValid } from '../../base/conference';
 import { VideoTrack } from '../../base/media';
 import { getLocalVideoTrack } from '../../base/tracks';
-import { generateRoomWithoutSeparator } from '../../base/util';
+
+import { generateRoomWithoutSeparator } from '../roomnameGenerator';
 
 /**
  * Base (abstract) class for container component rendering the welcome page.