Log Message:
bbdb2: Drop emacs28 from ACCEPTED

because it was reported failing after default was changed to 28.

Reorganize EMACS_VERSIONS_ACCEPTED to make it eaiser to edit; NFCI.

(It is true that I have no idea if this works for 27, and it is true
that this is old and should likely be deleted.  But that was true
before this edit also.)