remove forum lib, re #3505

git-svn-id: svn://develop.studip.de/studip/trunk@26684 c5b85792-5220-0410-ad23-ed5b6b8ad999
adjust cronjob scheduler to changes in [26668], prevents fatal error, re #3425

git-svn-id: svn://develop.studip.de/studip/trunk@26685 c5b85792-5220-0410-ad23-ed5b6b8ad999