Remove Shut Down from Login Window
Solution 1:
I don't know what the defaults write command is, but Mac Pilot can do this by setting this:
I just confirmed it works in 10.11.5 without needing a reboot.
Update
I figured out the defaults write:
sudo defaults write /Library/Preferences/com.apple.loginwindow ShutDownDisabled -bool true
Afterwards, the command
sudo defaults read /Library/Preferences/com.apple.loginwindow ShutDownDisabled
should equal 1.
Solution 2:
In Terminal type this:defaults write com.apple.loginwindow ShutDownDisabled -true to hide the Shutdown option.
To restore it again, type:defaults write com.apple.loginwindow ShutDownDisabled -false