To uninstall diffstat just follow these instructions.
/debian/stretch/main///install/index.html produces graph of changes introduced by a diff file Debian 9.0 devel 1.61-1+b1
sudo apt-get remove diffstat
Which will remove just the diffstat package itself.
sudo apt-get remove --auto-remove diffstat
This will remove the diffstat package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for diffstat then this will work.
sudo apt-get purge diffstat
Or similarly, like this diffstat
sudo apt-get purge --auto-remove diffstat
|Description||produces graph of changes introduced by a diff file|