Clean up erroneous WordPress releases and branches

Over time, some erroneous WordPress releases or branches were accidentally created:

  • 5.4-RC3-47470. This should have been a nightly bump instead.
  • 4.9.8-beta1-43498. This too should have been a nightly bump.
  • 4.2.26 branch on git://develop.git.wordpress.org/ mirror. This should have been a tag instead, and is already deleted on Core SVN, but still exists in the Git mirror and shows up on GitHub.

Would it be possible to clean them up to avoid confusion?

#prio3