Reduce @viewport to main feature; mark removal/deprecation

[rachelandrew]

Updating BCD for deprecated @viewport as described in mdn/sprints#3404 (comment)

[Elchi3]

I think reducing this to just the @viewport main feature is fine even if the sub features don't yet meet the removal requirements. (not yet 2 years gone per https://github.com/mdn/browser-compat-data/blob/master/docs/data-guidelines.md#removal-of-irrelevant-features)

The only blocking thing would be to do something with the MDN sub pages like
https://developer.mozilla.org/en-US/docs/Web/CSS/@viewport/max-width

Should we redirect these to https://developer.mozilla.org/en-US/docs/Web/CSS/@viewport?

[rachelandrew]

Should we redirect these to https://developer.mozilla.org/en-US/docs/Web/CSS/@viewport?

that would make sense to me, I don't think I can redirect or I would do it. I can move pages but that's all.

[Elchi3]

I've put the redirects in place for all sub pages of @viewport (there is a button in ckeditor, maybe it requires permissions?)

See https://wiki.developer.mozilla.org/en-US/docs/Web/CSS/@viewport/zoom$compare?locale=en-US&to=1655328&from=1645709 for how the change looks like.

[Elchi3]

It would be nice to also set the removal versions in Edge and Operas to signal that this is really gone, but we can also do that in a follow-up.

A question about standards track but otherwise LGTM.

[Elchi3]

Thanks Rachel! 👍