How to Uninstall System Apps by AppCleaner?
The remove the locks so that you can delete macOS system apps go to
AppCleaner -> Preferences -> General Tab
and Uncheck "protect default OSX Apps"

I just cleaned up garageband from macOS Sierra 10.12.5 which was shown as locked (system protected app) as shown in your image.

EDIT: As @leo said, please be warned that removing some system app like messages might break/ crash a whole set of applications or even the entire OS. SO please be careful about trying this