Bug 1259889 Part 2 [1] cannot be reverted cleanly, so I manually undo those
changes in this patch. That is, remove the ability for html.css to
invalidate dynamically since it was added specifically for details element.
Although reftest-stylo.list explicit mentions "DO NOT EDIT!", but I still
remove details pref from the file, since it doesn't harm to edit it anyway.
[1] https://hg.mozilla.org/mozilla-central/rev/30aaf3805b56
MozReview-Commit-ID: FsyTGQTxujh
