archive: optimize function lastActivity(), fixes #5283

git-svn-id: svn://develop.studip.de/studip/trunk@32808 c5b85792-5220-0410-ad23-ed5b6b8ad999
archive: move lastActivity() from functions to archive include file, re #5183

git-svn-id: svn://develop.studip.de/studip/trunk@32811 c5b85792-5220-0410-ad23-ed5b6b8ad999