ddclient is unmaintained as of 2023-07-04 [1]. This reverts changes related to commit 0bc2d3e42b8800e875f24973f999739297f1f502. [1]: <https://github.com/ddclient/ddclient/issues/528> * gnu/packages/dns.scm (ddclient): Remove variable. * gnu/packages/patches/ddclient-skip-test.patch: Remove file. * gnu/local.mk: Unregister it. Signed-off-by: Ludovic Courtès <ludo@gnu.org>