From the fink FAQ:
Q5.6: How can I uninstall all of Fink?
A: Almost all files installed by Fink are in /sw (or wherever
you chose to install it), except for a few exceptions.
Thus, in order to get rid of Fink, enter this command:
fink remove --recursive daemonic xinitrc
sudo rm -rf /sw
If you aren't planning to reinstall Fink you also will
want to remove the "source /sw/bin/init.csh" line you
added to your .cshrc file or the "source /sw/bin/init.sh"
line you added to your .bashrc file, whichever is appropriate
to your setup, using a text editor. If you had the xinitrc
package installed, then you will want to restore the original
/usr/X11/lib/X11/xinit/xinitrc, which has been backed up as
/usr/X11/lib/X11/xinit/xinitrc.YYYYMMDDhhmm, i.e. the
extension has a year, month, date, hour, and minute). If you
have more than one of these, the original one normally does
not mention sys-xinitrc-fink. Once you've found the right one,
you can use
sudo mv /usr/X11/lib/X11/xinit/xinitrc.YYYYMMDDhhmm \
replacing YYMMDDhhmm with the actual extension on your system.