Revert "Fix strong mode errors in dart:io."

tests/standalone/io/https_bad_certificate_test.dart

Index: tests/standalone/io/https_bad_certificate_test.dart
diff --git a/tests/standalone/io/https_bad_certificate_test.dart b/tests/standalone/io/https_bad_certificate_test.dart
index cafacfba15013b6f228b5cc67382413051be1989..7dc5aa2081c45ee72d35d5fb6cff3473d9fca9f5 100644
--- a/tests/standalone/io/https_bad_certificate_test.dart
+++ b/tests/standalone/io/https_bad_certificate_test.dart
@@ -71,8 +71,7 @@ Future runClient(int port,
   } catch (error) {
     Expect.notEquals(result, 'pass');
     if (result == 'fail') {
-      Expect.isTrue(error is HandshakeException ||
-          (callbackReturns is! bool && error is TypeError));
+      Expect.isTrue(error is HandshakeException);
     } else if (result == 'throw') {
       Expect.isTrue(error is CustomException);
     } else {