To uninstall racket-doc just follow these instructions.
/debian/stretch/main///install/index.html extensible programming language in the Scheme family (documentation) Debian 9.0 doc 6.7-3
sudo apt-get remove racket-doc
Which will remove just the racket-doc package itself.
sudo apt-get remove --auto-remove racket-doc
This will remove the racket-doc package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for racket-doc then this will work.
sudo apt-get purge racket-doc
Or similarly, like this racket-doc
sudo apt-get purge --auto-remove racket-doc
|Description||extensible programming language in the Scheme family (documentation)|