Correcting metadata path mapping.

Correcting metadata path mapping after removal of redundant metatadata directory.
https://github.com/artefactual/archivematica/commit/8f1ce7f4fe181bf524e5995d5b1f1aa481bdb029
https://github.com/artefactual/archivematica/commit/004109473bd4615c57ca98b4a08f308518e7c3f4
refs #4596
refs #4528