[GUI] removed sound group from the communication pref. page

The group was a left over of patch
http://saros-build.imp.fu-berlin.de/gerrit/#/c/1282/ which found a new
place in another preference page.

Change-Id: I7c1e0a87b629138b1a1ca3a31239064d51809565
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1290
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>