Remove `ci_fix_for_runner_cache_prefix ` feature flag

What does this MR do and why?

Describe in detail what your merge request does and why.

The purpose of this MR is to remove the feature flag ci_fix_for_runner_cache_prefix introduced in this MR.

It was successfully rolled out globally in: #404710 (closed)

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 #404710 (closed)