exchange-format: Drop 2.1.0 support, leaving 2.1.1 as the only version
Now that function-orchestrator and function-evaluator have switched to the 2.1.1 exchange format and deployed in production, the 2.1.0 module files, integration test, JS test file, and test_data/exchange_format{,_expected}/ fixtures can all be removed.
Bug: T416161
Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com