Remove summarize_diff_abstraction_layer feature flag
What does this MR do and why?
It's been a week since the feature flag has been enabled gloablly on production and no major issues were found related to the refactoring of feature to use the abstraction layer.
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
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I have evaluated the MR acceptance checklist for this MR.
Related to #423209 (closed)