Why was the “Lock device” shortcut removed?
Long story short, we received a notice from Google to remove this functionality from Action Launcher.
We are looking at how we can continue to offer similar functionality without upsetting Google. Thanks for your understanding and patience while this happens.
Some Action Launcher users opt to use an app called Greenify, which provides quasi-screen off behavior. This, or a similar app, may be of interest to you in the meantime.