Fix some edge cases when handling removal / reconstruction of table captions and col groups.
Being the last caption is not enough to remove an anonymous table (and
table wrapper).
Differential Revision: https://phabricator.services.mozilla.com/D216587
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1907789
gecko-commit: 96acf0534436cec34e18f7078e206873339a31d5
gecko-reviewers: dholbert