[BE] delete GHA generated workflow files before regen (#63148)
Summary:
Unlike circle which all workflow goes in one file, GHA legacy generated files will stay silently in once's PR. e.g. when we change build_environment name and that's not ideal.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63148
Reviewed By: bdhirsh
Differential Revision: D30283382
Pulled By: walterddr
fbshipit-source-id: ffdd5bf9561dd38499052855a12ee5cf838a20b0
Author
Rong Rong (AI Infra)
