$ sudo apt-get remove icinga2 

Uninstall icinga2 including dependent package

If you would like to remove icinga2 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove icinga2 

Use Purging icinga2

If you use with purge options to icinga2 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge icinga2 

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 icinga2 

See Also,