no need to rebuild the collection if exists

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1447475 13f79535-47bb-0310-9956-ffa450edef68
this optimisation was very crappy in fact so remove it: too much synchronization were needed

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1447476 13f79535-47bb-0310-9956-ffa450edef68