bugfix: EventList::remove(event) must deal correctly with active events

before: active events were not properly deleted
        (in both cases, ev == 0 and ev != 0)
after: deficiencies repaired; simpler code
side-effect: doesn't return whether the event was found anymore
             (can be re-added at a later time)

git-svn-id: https://www4.informatik.uni-erlangen.de/i4svn/danceos/trunk/devel/fail@1024 8c4709b5-6ec9-48aa-a5cd-a96041d1645a