Update targets/ dir to match current artifacts in metadata

[jku]

• remove obsolete revocation/revocation.list and rekor.0.pub: Neither is included in current TUF metadata
• add registry.npmjs.org/keys.json: This file is included in the current metadata

targets/ now matches the metadata in repository/repository and artifacts in repository/repository/targets (apart from trusted_root.json that has been modified in targets/ after the last signing event).

This is part of #1247 (tuf-on-ci uses this directory to generate new targets metadata: this means it should not contain obsolete files)

[jku]

I'll try to kick DCO with close & reopen but may have to make a commit message if that does not work