move term_variables to builtins

src/prolog/lib/terms.pl

@@ -1,17 +1,9 @@
-:- module(terms, [term_variables/2, numbervars/2, numbervars/3]).
-
-term_variables(Term, Vars) :- '$term_variables'(Term, Vars).
+:- module(terms, [numbervars/2]).
 
 numbervars(Term, N) :-
     integer(N),
     term_variables(Term, Vars),
     numberlist(Vars, N, N1).
-    
-numbervars(Term, N0, N) :-
-    integer(N0),
-    integer(N),
-    term_variables(Term, Vars),
-    numberlist(Vars, N0, N).
 
 numberlist([], N,N).
 numberlist(['$VAR'(N0)|Vars], N0,N) :-