Remove unnecessary imports (#1523)

The check is now stronger and surfaces imports that are only exposing
symbols that are also available through other imports.
diff --git a/pkgs/test_core/lib/src/runner/vm/platform.dart b/pkgs/test_core/lib/src/runner/vm/platform.dart
index 0083272..636792d 100644
--- a/pkgs/test_core/lib/src/runner/vm/platform.dart
+++ b/pkgs/test_core/lib/src/runner/vm/platform.dart
@@ -13,8 +13,6 @@
 import 'package:stream_channel/isolate_channel.dart';
 import 'package:stream_channel/stream_channel.dart';
 import 'package:test_api/backend.dart'; // ignore: deprecated_member_use
-import 'package:test_api/src/backend/runtime.dart'; // ignore: implementation_imports
-import 'package:test_api/src/backend/suite_platform.dart'; // ignore: implementation_imports
 import 'package:test_core/src/runner/vm/test_compiler.dart';
 import 'package:vm_service/vm_service.dart' hide Isolate;
 import 'package:vm_service/vm_service_io.dart';