Remove the `container_expiration_policies_historic_entry` feature flag

🐟 Context

container_expiration_policies_historic_entry is a feature flag scoped to Projects we used to slowly allow more and more projects to have cleanup policies.

Executing cleanup policies is not an easy task and given the scale of gitlab.com, when we introduced them, we only allowed new projects to have cleanup policies.

Slowly but surely we allowed existing old project to have policies using this feature flag and a % deployment.

This feature flag has been enabled globally 2 months ago on gitlab.com.

Now is the time where we remove this feature flag from the codebase.

Here is the rollout issue: #262639+.

Lastly, note that this is a feature flag within a feature flag 🎎

As such, the proper changelog will be created when the "global" feature flag is enabled by default. See !80815 (merged).

🔍 What does this MR do and why?

• Remove the container_expiration_policies_historic_entry feature flag from the codebase.
• Update the related specs.

⚠ Note for the maintainer: do not merge this MR if gitlab-com/gl-infra/production#6411 (closed) is not closed. Product change has been carried out and issue is now closed. We're clear to merge this MR. 🚀

🖼 Screenshots or screen recordings

n / a

🔨 How to set up and validate locally

We don't really have a way to check this feature flag cleanup.

🛃 MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.