[STF|API] removed ScreenSharing and VOIP support

The features were removed, so remove them also from the test framework.

Change-Id: Ibdf05d1403ff5015d23628e340eb9be86bf374ee
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1341
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>