See, I told you not to look.

Open a Terminal

  $ gksudo iptables -D OUTPUT -j SelfControl
  $ gksudo iptables -F SelfControl
  $ gksudo iptables -X SelfControl

These will be done along with other file removals when you
un-install the package with synaptic/aptitude/dpkg etc.  But
if you don't remove the rc script before rebooting it might
re-enable the iptables chains and current blocks.

  $ gksudo update-rc.d -f selfcontrol remove
  $ gksudo rm -rf /etc/init.d/selfcontrol /etc/selfcontrol

  $ gksudo dpkg --purge selfcontrol  # libselfcontrol-perl for old installs.

The 'at' jobs will just run anyway and fail.