$ sudo apt-get remove cython3 

Uninstall cython3 including dependent package

If you would like to remove cython3 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove cython3 

Use Purging cython3

If you use with purge options to cython3 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge cython3 

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 cython3 

See Also,