[gardening] Cleanup stress test list.

Follow-up to 1d684cd which deleted the test.

Fixes #59705

Change-Id: I11ddaacf75af2234e6228f80f569b47d3f3b9490
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/400360
Commit-Queue: Alexander Aprelev <[email protected]>
Reviewed-by: Jessy Yameogo <[email protected]>

Author: aam

runtime/tests/concurrency/stress_test_list.json

@@ -600,7 +600,6 @@
   "../../../tests/language/abstract/method_test.dart",
   "../../../tests/language/abstract/object_method_test.dart",
   "../../../tests/language/abstract/override_adds_optional_args_test.dart",
-  "../../../tests/language/abstract/syntax_runtime_test.dart",
   "../../../tests/language/accessor_conflict/export2_test.dart",
   "../../../tests/language/accessor_conflict/export_test.dart",
   "../../../tests/language/accessor_conflict/import2_test.dart",