Update microformats spec page with actual usage

[mjankowski]

Basically a followup on the large deprecation/removal notice on the top of the page. Seems safe to remove this given no support for ~5 versions / multiple years.

Notes and more to do:

• There is still support for MF classes in the sense that the AP content sanitizer will preserve some of them. This is mentioned in the AP processing section of the docs (and should stay), and I believe is still accurate re: the code, but could double check that and update docs if needed.
• I will do a pass through the codebase for any MF-style classes which were left behind and could be removed (which I think is safe as long as they are not there for styling or behavior purposes, or in some way involved with the AP content preservation, etc)

[andypiper]

Per conversation with @trwnh - I think (?) the preference would be to clarify what microformat elements do remain, and how they are used; maybe then to fold this information somewhere else rather than giving an impression of broad microformats support, or simply to cut this down.

[mjankowski]

Updated to keep the page, removing unused MFs, preserving used MFs

Followup - there's an .e-content CSS style in the app, but no actual usage I don't think. Will do separate PR in app for that.