Revert "fix: type-var bug"

This reverts commit 6fff895.

Author: mtshiba

crates/erg_compiler/context/unify.rs

@@ -2324,7 +2324,7 @@ impl Context {
             let new_sub = self
                 .eval_t_params(maybe_sub.clone(), self.level, loc)
                 .map_err(|(_, errs)| errs)?;
-            if maybe_sub.is_unbound_var() && new_sub != Never && &new_sub != maybe_sub {
+            if new_sub != Never && &new_sub != maybe_sub {
                 maybe_sub.link(&new_sub, unifier.undoable);
             }
             let new_super = self

crates/erg_compiler/ty/mod.rs

@@ -3702,7 +3702,7 @@ impl Type {
             Type::FreeVar(fv) if fv.is_linked() => {
                 fv.crack().destructive_coerce();
             }
-            Type::FreeVar(fv) if !fv.is_generalized() && fv.is_unbound_and_sandwiched() => {
+            Type::FreeVar(fv) if fv.is_unbound_and_sandwiched() => {
                 let (sub, _sup) = fv.get_subsup().unwrap();
                 if !sub.contains_tvar(fv) {
                     sub.destructive_coerce();