Remove an unused VOP %make-symbol on x86-64.

Remove an unused VOP %make-symbol on x86-64.

%make-symbol is handled by define-primitive-object now.
The old VOP was copied into alloc.lisp during the x86_64 port, got
removed from x86 before the merge. It wasn't even ported to x86-64,
and was never invoked during the 9 years it has been sitting there.

Also remove fast_random_state variable from the C runtime, it was used
by the VOP.