EZP-23639: told dfs cleanup to clean dfs, not var

> See [EZP-23639](https://jira.ez.no/browse/EZP-23639)

I'm very confused by this one. If a file was created on the NFS, running `bin/php/dfscleanup.php -B -D` would find the extra file, and throw a warning when trying to unlink it.

Reason was simple: we were doing an unlink, meaning that the file was deleted from the var folder, while it was found on NFS. The fix is easy, but the question is: did it ever work ?