User cleanup should not remove users just because the DN has changed

Currently the user cleanup checks only if there is a user (or in fact some object) for the DN given in the XWiki user profile page.

In case the user is moved to a different OU, which might include giving it a different DN, that user profile might be removed on a wrong assumption, if the user does not log in between the time the DN is changed and the user cleanup job runs. If case the DN does not match, one should instead use the filter that is also used at login to find the user before removing the user profile.