Remove unnecessary assertion for reference error

compiler/rustc_hir_analysis/src/check/check.rs

@@ -1637,7 +1637,6 @@ fn check_type_alias_type_params_are_used<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalD
     let ty = tcx.type_of(def_id).instantiate_identity();
     if ty.references_error() {
         // If there is already another error, do not emit an error for not using a type parameter.
-        assert!(tcx.dcx().has_errors().is_some());
         return;
     }
 

tests/ui/wf/ice-hir-wf-issue-135341.rs

@@ -0,0 +1,4 @@
+type A<T> = B;
+type B = _; //~ ERROR the placeholder `_` is not allowed within types on item signatures for type aliases
+
+fn main() {}

tests/ui/wf/ice-hir-wf-issue-135341.stderr

@@ -0,0 +1,9 @@
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for type aliases
+  --> $DIR/ice-hir-wf-issue-135341.rs:2:10
+   |
+LL | type B = _;
+   |          ^ not allowed in type signatures
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0121`.