$ sudo apt-get remove libonig2 

Uninstall libonig2 including dependent package

If you would like to remove libonig2 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove libonig2 

Use Purging libonig2

If you use with purge options to libonig2 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge libonig2 

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 libonig2 

See Also,