Adopt horde/compress PSR-4

[ralflang]

Compress is used in Horde_Backup_Reader::decompress - Use Horde\Compress\Driver\Tar instead.
Compress is used in Horde_Backup_Reader::decompress - Use Horde\Compress\Driver\Zip instead.
Compress is used in Horde_Backup_Writer::compress - Use Horde\Compress\Driver\Tar instead.
Compress is used in Horde_Backup_Reader_CompressIterator_Zip::current - Use Horde\Compress\Driver\Zip instead.

See https://github.com/horde/Compress/blob/FRAMEWORK_6_0/doc/UPGRADING.md