Stop testing the legacy architecture (#51738)

Summary:
Following up the announcement made at AppJS, this change stops testing the legacy architecture in our CI

## Changelog:
[Internal] - Stop testing the legacy architecture in CI

Pull Request resolved: https://github.com/facebook/react-native/pull/51738

Test Plan: waiting for GHA

Reviewed By: cortinico

Differential Revision: D75791359

Pulled By: cipolleschi

fbshipit-source-id: cb3159338835f49589fa6f495cfb9f47750825fe