Make Daemon Memory Killer be the default for Sidekiq

What does this MR do?

We have two Sidekiq memory killers: legacy memory killer and daemon memory killer.

We should remove the legacy memory killer in the long term, because:

• legacy memory killer is expected to be replaced by daemon memory killer
• maintain two memory killers requires extra effort
• maintain two memory killers makes configuration complex, sometimes it is confusing when diagnosing issues, one example is: https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/10930#note_386967266

Before remove legacy memory killer, we need to make daemon memory killer be the default for Sidekiq.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #232765 (closed)