tests: remove obsolete test metadata

[lukpueh]

Legacy python-tuf included a deployment recommendation of using metadata and metadata.staged directories. This recommendation does not exist anymore.

I think, we can safely remove the related test metadata directory tests/repository_data/repository/metadata.staged, which is no longer used and has become out of sync.

[lukpueh]

Highjacking the issue...

More obsolete test data:

• tests/repository_data/project (left-over from removed developer_too.py, #1790)
• tests/repository_data/map.json (needed for TAP4, which is not supported in python-tuf)