Remove the xtrabackup_logfile from the archive

[deviantony]

In the case of a full backup only, as the backup is already prepared using the --apply-log option there is no need to keep the xtrabackup_logfile in the backup archive.

[alexanderilyin]

Just found it on my master in datadir:

442M	/data/***/xtrabackup_logfile

It would be nice it could be automatically removed/excluded if it's not required to have it to save some disk space.