Remove Expect from core library.

tests/language/type_checks_in_factory_method_test.dart

Index: tests/language/type_checks_in_factory_method_test.dart
diff --git a/tests/language/type_checks_in_factory_method_test.dart b/tests/language/type_checks_in_factory_method_test.dart
index b0056d7076941445332707e12822a342f0fd3b47..4402fd6c5343de11fd26e0c12b0f47f0373d9a1d 100644
--- a/tests/language/type_checks_in_factory_method_test.dart
+++ b/tests/language/type_checks_in_factory_method_test.dart
@@ -4,6 +4,8 @@
 // VMOptions=--enable_checked_mode
 // Tests the type checking when passing code into closure from inside a factory method
 
+import "package:expect/expect.dart";
+
 abstract class Foo<T> {
   factory Foo.from() = Bar<T>.from;
 }