$ sudo apt-get remove libgnatcoll1.6 

Uninstall libgnatcoll1.6 including dependent package

If you would like to remove libgnatcoll1.6 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove libgnatcoll1.6 

Use Purging libgnatcoll1.6

If you use with purge options to libgnatcoll1.6 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge libgnatcoll1.6 

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 libgnatcoll1.6 

See Also,