Move skip_release from librarian config to release_please

We currently have skip_release blocks for certain libraries under [librarian.yaml](https://github.com/googleapis/google-cloud-python/blob/main/librarian.yaml). We should move them under [release-please-individual-config.json](https://github.com/googleapis/google-cloud-python/blob/main/release-please-individual-config.json), now that we have migrated back to the release-please tool