Remove executable argument forwarding in tests

Similar to #2528

This case of argument forwarding existed since the test runner was first
written. It's not clear exactly why it was necessary, so removing it if
no current tests break.

Author: natebosch

pkgs/test/test/io.dart

@@ -142,10 +142,6 @@ Future<TestProcess> runDart(
   String? packageConfig,
 }) async {
   var allArgs = <String>[
-    ...Platform.executableArguments.where(
-      (arg) =>
-          !arg.startsWith('--package-root=') && !arg.startsWith('--packages='),
-    ),
     '--packages=${packageConfig ?? await Isolate.packageConfig}',
     ...args,
   ];