Fix testXfuncs to honor its first argument

Author: fingolfin

tst/testinstall/xfuncs.tst

@@ -2,7 +2,6 @@
 gap> START_TEST("xfuncs.tst");
 gap> testXfuncs := function(list, args...)
 >      local set, sum, prod;
->      list := CallFuncList(ListX, args);
 >      set := Set(list);
 >      if IsEmpty(list) then
 >        sum := fail; prod := fail;