[LOCAL] Revert Podfile.lock error handling in CI script, remove same step from new workflow

It looks like this always failed (recent example from RC3: https://app.circleci.com/pipelines/github/facebook/react-native/42625/workflows/911813aa-8c1c-4c7f-8382-5d67d3551923/jobs/1396276), but since #43513 this now correctly raises as an error to CircleCI.

To unblock our release:
- Revert.
- Also remove "Updating RNTester Podfile.lock" entirely from `prepare_release_new` job — technically this isn't in the critical path for making a release, but is part of consistent branch state _post release_.

Changelog: [Internal]