Automatically remove all "awaiting" tags when closing/merging a PR

I have some closed/merged PRs that have one of the "awaiting" on them, and I guess it's common to forget to remove tags. I believe these are unnecessary entries that clutter the view when you people filter the list.

I thought they could be automatically removed when a PR is closed/merged. They aren't useful anymore, right?

If this is deemed useful, I could make a PR.