$ sudo apt-get remove i3lock 

Uninstall i3lock including dependent package

If you would like to remove i3lock and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove i3lock 

Use Purging i3lock

If you use with purge options to i3lock package all the configuration and dependent packages will be removed.

$ sudo apt-get purge i3lock 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove i3lock 

See Also,