ipset: drop obsolete patch

Since commit 0552a367 ("Remove --{enable, disable}-debug configure flags.")
we do not pass --enable-debug to configure script. The patch to remove -Werror
in this case is thus no longer needed.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>