dfmc-modeling: Fix primitive definitions to match reality

Fix various out-of-date definitions for booted compiler primitives to
match how they are implemented in the back-ends and used within the
libraries.

* sources/dfmc/modeling/primitives.dylan
  (primitive primitive-set-accessor-method-xep): Add the missing what
   parameter to the primitive's signature.
  (primitive primitive-apply): Correct the signature to show that
   arguments are passed as a <simple-object-vector>.
  (primitive primitive-values): Correct the signature to show that
   arguments are passed as a <simple-object-vector>.