Fix warnings of dead code

src/machine/unify.rs

@@ -453,30 +453,6 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         }
     }
 
-    fn unify_big_num<N>(&mut self, n1: TypedArenaPtr<N>, value: HeapCellValue)
-    where
-        N: PartialEq<Rational> + PartialEq<Integer> + PartialEq<i64> + ArenaAllocated,
-    {
-        if let Some(r) = value.as_var() {
-            Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
-            return;
-        }
-
-        match Number::try_from(value) {
-            Ok(n2) => match n2 {
-                Number::Fixnum(n2) if *n1 == n2.get_num() => {}
-                Number::Integer(n2) if *n1 == *n2 => {}
-                Number::Rational(n2) if *n1 == *n2 => {}
-                _ => {
-                    self.fail = true;
-                }
-            },
-            Err(_) => {
-                self.fail = true;
-            }
-        }
-    }
-
     fn unify_big_integer(&mut self, n1: TypedArenaPtr<Integer>, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
             Self::bind(self, r, typed_arena_ptr_as_cell!(n1));