chore(librarian): Add forward slash to remove regex

[parthea]

This PR adds a forward slash to the remove_regex to provide clarity that the regex is for the full directory name not partial name.
For example, for google-cloud-compute , where there also exists google-cloud-compute-v1beta

We would have

    remove_regex:
      - packages/google-cloud-compute/

which would only match google-cloud-compute

instead of

    remove_regex:
      - packages/google-cloud-compute

Which would match both google-cloud-compute and google-cloud-compute-v1beta