Performance backup garbage collection potentially tries to delete same file multiple times

A cleaning task of backup.inc.php reads the file contents of a domains backup directory.

Those get compared against web_backup database table.

Backup filenames that should exist are read from web_backup table.

If there are duplicates in that table, the temp array of files to delete will have them, too ( no SELECT DISTINCT filename).

The author wanted to remove those duplicates using array_unique.

It never effectively was used, as this function does not receive the value by ref but returns a new value.

This code will take the return value and use it in the comming loop which does the actual deletion.

Rare case, keeping old code does not harm.