Since it allows to animate display, which is not good.

This is a regression from:

  https://hg.mozilla.org/mozilla-central/rev/6884ba750aa3

Actually I wonder if the logic shouldn't be the other way around, i.e., a
shorthand is animatable if all the longhands are, not if just one.

In any case this rolls back to the previous behavior, should we do that, it
should be another bug.

Differential Revision: https://phabricator.services.mozilla.com/D14632