Remove legacy memory killer

What does this MR do and why?

It removes legacy memory killer that was deprecated 2 years ago and replaced with daemon sidekiq memory killer.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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 #372765 (closed)