Remove irrelevant "dom.animations-api.core.enabled" flag

[queengooborg]

This PR removes the now-irrelevant dom.animations-api.core.enabled flag from API data.

[foolip]

I don't think that removing parts of the flag data is really improving the data or its maintainability. I'd prefer to leave it in until the entry can be simplified to contain no flag data at all.

[queengooborg]

I was thinking that since this particular flag had been removed from AnimationTimeline already (#9713), we should remove it from the other files containing data for it as well. Happy to wait until we can remove more flags, though.

[foolip]

OK, I'm a sucker for consistency :)

[foolip]

In addition to missing "dom.css_pseudo_element.enabled" entried for Firefox for Android, there's also the issue of Firefox for Android dropping support for flags entirely recently.

[queengooborg]

Added version_removed in all the other locations! I also added a few to Firefox Desktop in the process (since we're here, we might as well tidy up that data a bit, right?).