$ sudo apt-get remove grass-gui 

Uninstall grass-gui including dependent package

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

$ sudo apt-get remove --auto-remove grass-gui 

Use Purging grass-gui

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

$ sudo apt-get purge grass-gui 

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 grass-gui 

See Also,