$ sudo apt-get remove gimp-gap 

Uninstall gimp-gap including dependent package

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

$ sudo apt-get remove --auto-remove gimp-gap 

Use Purging gimp-gap

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

$ sudo apt-get purge gimp-gap 

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 gimp-gap 

See Also,