Cleanup GitHub actions (NRL weekly builds)

[climbfuji]

Description

NRL is switching from the weekly build scripts to util/nrl/batch_install.sh for CI testing, including in GitHub actions. This is all done in the NRL Enterprise GitHub.

For more than a year, NRL was the only user and developer of GitHub actions CI testing with the weekly build scripts. EPIC uses Jenkins, EMC uses cron. Thus, this PR removes .github/actions/Nightly_*.yaml and util/weekly_build/sites/<host>.yaml for the NRL hosts.

Dependencies

None

Issues addressed

Closes #1683

Applications affected

None

Systems affected

NRL sites

Testing

• CI: Note whether the automatic tests (GitHub actions tests that run automatically for every commit) pass or not
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (provide explanation if necessary)
• New tests added: List and describe any new tests added to GitHub actions
  • ...
• Additional testing: Add information on any additional tests conducted
  • ...

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the spack-stack wiki will be made when this PR is merged