[INTERNAL] removed unnecessary listener

It seems that the listener for the EditorPlugin was used to update the
viewer on color changes. As we do not modify the EditorPlugin preference
store during runtime anymore the listener became obsolete.

Change-Id: I4dbcce00c784ffce7caac4c3675ab586d6de933f
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1173
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>