Revert "Enqueue superclasses instead of supertypes."

tests/compiler/dart2js/type_combination_test.dart

Index: tests/compiler/dart2js/type_combination_test.dart
diff --git a/tests/compiler/dart2js/type_combination_test.dart b/tests/compiler/dart2js/type_combination_test.dart
index 5d8e18d609d46349b9572f07259236746b91daa0..834f900e3dc727b83253204961d9a792d4f7b03b 100644
--- a/tests/compiler/dart2js/type_combination_test.dart
+++ b/tests/compiler/dart2js/type_combination_test.dart
@@ -741,8 +741,6 @@ void main() {
     });
     compiler.enqueuer.resolution.registerInstantiatedType(
         compiler.coreTypes.mapType(), compiler.globalDependencies);
-    compiler.enqueuer.resolution.registerInstantiatedType(
-        compiler.coreTypes.functionType, compiler.globalDependencies);
     compiler.world.populate();
 
     // Grab hold of a supertype for String so we can produce potential