Remove context_commits feature flag

What does this MR do and why?

The feature has been enabled by default on self-managed installs for multiple milestones and has been enabled on production for a while and no blocking issues were found.

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.

Related to #320757 (closed)