Revert "Collect the types used in is-checks in the resolver phase."

lib/compiler/implementation/util/link_implementation.dart

Index: lib/compiler/implementation/util/link_implementation.dart
diff --git a/lib/compiler/implementation/util/link_implementation.dart b/lib/compiler/implementation/util/link_implementation.dart
index 1331f2e970be92f7a10e53a726c57d57aee31f65..a237a307a12f92ac39e9f09a45101096b4434d21 100644
--- a/lib/compiler/implementation/util/link_implementation.dart
+++ b/lib/compiler/implementation/util/link_implementation.dart
@@ -70,11 +70,6 @@ class LinkTail<T> implements EmptyLink<T> {
   bool isEmpty() => true;
 
   void forEach(void f(T element)) {}
-
-  bool equals(other) {
-    if (other is !Link<T>) return false;
-    return other.isEmpty();
-  }
 }
 
 class LinkEntry<T> implements Link<T> {
@@ -139,19 +134,6 @@ class LinkEntry<T> implements Link<T> {
       f(link.head);
     }
   }
-
-  bool equals(other) {
-    if (other is !Link<T>) return false;
-    Link<T> myElements = this;
-    while (!myElements.isEmpty() && !other.isEmpty()) {
-      if (myElements.head != other.head) {
-        return false;
-      }
-      myElements = myElements.tail;
-      other = other.tail;
-    }
-    return myElements.isEmpty() && other.isEmpty();
-  }
 }
 
 class LinkBuilderImplementation<T> implements LinkBuilder<T> {