[GUI] Deleted preferences placeholder text

Franz and I decided that it would be best to
completely delete the placeholder text at this 
point since the preferences menu is 
self-explanatory.

Change-Id: I5c4a3a6c150011214e569023be78671434857391
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/2006
Tested-by: Jenkins CI
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>