Revert "Support runtime check of function types."

sdk/lib/_internal/compiler/implementation/util/link_implementation.dart

Index: sdk/lib/_internal/compiler/implementation/util/link_implementation.dart
diff --git a/sdk/lib/_internal/compiler/implementation/util/link_implementation.dart b/sdk/lib/_internal/compiler/implementation/util/link_implementation.dart
index 6743738f2a0fce19217915bd829a77b0795ee97e..4b0a61846a05e60b5d43ceb6c11ec6079b06f2d1 100644
--- a/sdk/lib/_internal/compiler/implementation/util/link_implementation.dart
+++ b/sdk/lib/_internal/compiler/implementation/util/link_implementation.dart
@@ -110,9 +110,9 @@ class LinkBuilderImplementation<T> implements LinkBuilder<T> {
 
   LinkBuilderImplementation();
 
-  Link<T> toLink([Link<T> tail = const Link()]) {
-    if (head == null) return tail;
-    lastLink.tail = tail;
+  Link<T> toLink() {
+    if (head == null) return const Link();
+    lastLink.tail = const Link();
     Link<T> link = head;
     lastLink = null;
     head = null;