Fix build for throwsStateError: remove duplicate definitions in other tests.

utils/tests/pub/curl_client_test.dart

Index: utils/tests/pub/curl_client_test.dart
diff --git a/utils/tests/pub/curl_client_test.dart b/utils/tests/pub/curl_client_test.dart
index ba57e21937838eb2d7062e02d6c694f7314b2a42..924e994ec4d775187e4dc718928e49b17e45461f 100644
--- a/utils/tests/pub/curl_client_test.dart
+++ b/utils/tests/pub/curl_client_test.dart
@@ -168,19 +168,6 @@ class _Parse extends BaseMatcher {
   }
 }
 
-// TODO(nweiz): remove this once it's built in to unittest (issue 7922).
-/// A matcher for StateErrors.
-const isStateError = const _StateError();
-
-/// A matcher for functions that throw StateError.
-const Matcher throwsStateError =
-    const Throws(isStateError);
-
-class _StateError extends TypeMatcher {
-  const _StateError() : super("StateError");
-  bool matches(item, MatchState matchState) => item is StateError;
-}
-
 /// A matcher for HttpExceptions.
 const isHttpException = const _HttpException();