Email addresses and ftp:// links leave behind bare <a> tags
Due to the switch away from Bleach's linkification to cmark-gfm's autolink extension in f1d2e0ae:
autolink initially creates links for email addresses and
ftp:// addresses, but the sanitization removes them due to the protocol whitelist, leaving behind a bare
<a> tag. This will still appear to be a link but not actually link anywhere.
If I decide to continue using autolink and not switch back to Bleach linkification once the issues are fixed, we should strip these bare
<a> tags out of the HTML.