`--internal_ci` has been deprecated and unused for 6 years. https://github.com/grpc/grpc/pull/16635 Closes #37261 COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37261 from drfloob:rm-internal-ci-flag 486eb1cc44 PiperOrigin-RevId: 657276079
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