src/method-proto.lisp (make-trampoline): Ignore unused keyword pointers.

src/method-proto.lisp (make-trampoline): Ignore unused keyword pointers.

If we're not going to need a keyword pointer (because the applicable
methods have no keyword arguments) then ignore it explicitly.  (We can't
just omit the arguments, because direct-method functions may have to
work as part of an effective method which /does/ have keyword arguments
-- maybe even downstream -- and the trampoline functions must have the
same signature either way.)