Make Daemon Memory Killer be the default for Sidekiq

Follow up https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/10930#note_387183013.

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.

Some updates to allow people to find relative information easier in the future:

• from the MR discussion !41847 (comment 412155912), Gitlab.com VM is using the legacy memory killer. But we do not seem much impact to make daemon memory killer as default one.
• what is the potential impact, and what is the benefit of daemon memory killer: !41847 (comment 412020465)