Design doc: drop link to obsolete patches.

This is a follow-up on commit:7a1d01de, that
removed these patches.

wiki/src/contribute/design.mdwn

@@ -1123,9 +1123,6 @@ manual configuration.
 OpenPGP support is provided by the Enigmail addon.
 
 - [[!tails_gitweb config/chroot_local-includes/etc/thunderbird/pref/thunderbird.js]]
-- [[!tails_gitweb config/chroot_local-patches/torbirdy-0001-secure-autoconfig-compat.diff]]
-- [[!tails_gitweb config/chroot_local-patches/torbirdy-0001-secure-autoconfig-compat.diff]]
-- [[!tails_gitweb config/chroot_local-patches/torbirdy-0002-secure-autoconfig-POP-defaults.diff]]
 - [[!tails_gitweb_dir config/chroot_local-includes/etc/skel/.thunderbird]] is copied to
   the user's `$HOME` at boot time
 - [[!tails_gitweb config/chroot_local-includes/usr/local/bin/thunderbird]]