[INTERNAL] removed skipSync logic

The preference option to skip synchronization for projects was removed a
long time ago. Removed the logic that actually used this option.

Change-Id: I5334d2249e8d2345fcddf39578582020aaf984ff
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1151
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>