Remove legacy Sidekiq Daemon Memory Killer.

What does this MR do and why?

Removes legacy Sidekiq Daemon Memory Killer.

We are already using backward-compatible Sidekiq Memory Watchdog for several releases by default. This is just a cleanup of unused code.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

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 #371500 (closed)