Fixed deleting old file versions owncloud/core/issues/3279

Should fix https://github.com/owncloud/core/issues/3279

$versionsName is always the original filename like:

/var/www/data/test/files_versions/test.txt

and $de is always the original filename with the version string appended like:

/var/www/data/test/files_versions/test.txt.v1368778304

This is causing a wrong link to unlink() like reported in the bugreport above.