How to disable lock-screen hotkey (Command-ctr-Q) in High Sierra?
The following worked for me:

Open "System Preferences", select "Keyboard", then "Shortcuts".

From the list of shortcut categories in the left-hand list, select "App Shortcuts".

Add (this is counter-intuitive since you want to disable an existing shortcut) a new shortcut using the "+" button:

Under "Menu Title", enter "Lock Screen" (this should be how the action appears on the "Apple" desktop menu).

Then under Keyboard Shortcut, enter a key combination that you can "sacrifice".  You could use something hard to type like Ctrl + Alt + Cmd + Shift + L.

You "save" the new Keyboard Shortcut (which actually overrides the previously invisible Ctrl + Cmd + Q shortcut) by closing the Keyboard preferences window.  

Now you should be able to enjoy Ctrl + Cmd + Q's awesome Emacs binding again.