Use specialized worker to refresh authorizations on project-group share update by default

What does this MR do and why?

Removes the feature flag specialized_worker_for_project_share_update_auth_recalculation , which was enabled fully on production on June 30, 2021 in milestone 14.1.

It has been more than 2 months that this change has been running on production without any trouble, so we can remove this feature flag from the codebase.

Rollout issue: #334234 (closed)

Screenshots or screen recordings

Current status of this feature flag in production & staging:

How to set up and validate locally

MR acceptance checklist

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