202012-update.md, dev-trials-feedback.md, howto.md: these seem like artifacts from the development process and/or Chromium Origin Trial process, which probably don't need to be maintained forever.
tag-security-privacy.md: TAG review has concluded, and this contains a lot of service-worker specific stuff
Note that I think keeping explainer.md is reasonable, or at least deleting it deserves a separate discussion.
docs/urlpattern.md: it's basically a redirect
mdn-drafts/QUICK-REFERENCE.md: subsumed by actual MDN docs, I think? https://developer.mozilla.org/en-US/docs/Web/API/URLPattern
202012-update.md, dev-trials-feedback.md, howto.md: these seem like artifacts from the development process and/or Chromium Origin Trial process, which probably don't need to be maintained forever.
tag-security-privacy.md: TAG review has concluded, and this contains a lot of service-worker specific stuff
Note that I think keeping explainer.md is reasonable, or at least deleting it deserves a separate discussion.