This directory is now effectively unused. Test specs now entirely handled via Starlark in //infra/config/. This directory still exists because:

1. A default (non-builder-specific) test spec directory needs to be defined for a Chromium config.
2. The Starlark-generated GN args need to be pointed to by an entry in angle_mb_config.pyl
3. trybot_analyze_config.json is not generated, so there is not much reason to move it under //infra/config/.