Remove unused API.

dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart

Index: dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart b/dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart
index bb7b7a94af0e4a51e80c3f23760c60f31fd1cc0a..ec6acab90c9457c5158cc736905f9ca17d50f1d4 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/types/forwarding_type_mask.dart
@@ -42,10 +42,6 @@ abstract class ForwardingTypeMask implements TypeMask {
     return forwardTo.containsOnlyNum(compiler);
   }
 
-  bool containsOnlyNull(Compiler compiler) {
-    return forwardTo.containsOnlyNull(compiler);
-  }
-
   bool containsOnlyBool(Compiler compiler) {
     return forwardTo.containsOnlyBool(compiler);
   }
@@ -74,10 +70,6 @@ abstract class ForwardingTypeMask implements TypeMask {
     return forwardTo.singleClass(compiler);
   }
 
-  Iterable<ClassElement> containedClasses(Compiler compiler) {
-    return forwardTo.containedClasses(compiler);
-  }
-
   TypeMask union(other, Compiler compiler) {
     if (this == other) {
       return this;
@@ -93,10 +85,6 @@ abstract class ForwardingTypeMask implements TypeMask {
     return forwardTo.intersection(other, compiler);
   }
 
-  bool understands(Selector selector, Compiler compiler) {
-    return forwardTo.understands(selector, compiler);
-  }
-
   bool needsNoSuchMethodHandling(Selector selector, Compiler compiler) {
     return forwardTo.needsNoSuchMethodHandling(selector, compiler);
   }