Sped ACL2(h) up a bit by eliminating a special variable.

Quoting a comment in (defvar *aokp* ...):

; Before Version_7.0, *aokp* was Boolean and a separate special variable,
; *attached-fn-called*, was used for holding a function symbol whose
; attachement has been called.  By folding that role into *aokp* we reduced the
; time for (defthm spec-body ...) in
; books/misc/misc2/reverse-by-separation.lisp from 188 seconds to 181 seconds,
; a savings of about 4%.

I might add a corresponding item to :doc note-7-0 after I get a bit
more data about the speed-up from this change.