Consider dropping "API" from shortTitle values

[tidoust]

C.f. web-platform-dx/web-features#545 (comment) for context.

As far as I remember, the shortTitle property was introduced for Bikeshed and CSS specifications to start with. I don't recall specific requests for API specifications, and I don't recall that we discussed keeping or dropping "API" from the title. As web-features adds short names, one guideline that seems to emerge, when spec titles are used, is to drop "API".

Worth doing it in browser-specs as well?