package/libxml2: Remove autoreconf

package/libxml2: Remove autoreconf

Autoreconf is not necessary since we do not patch this package anymore.

LIBXML2_AUTORECONF was added back in 2012
https://git.busybox.net/buildroot/commit/package/libxml2?id=aa5d9ba3b86f21be934fdb436525a833bf120305

and apparently not removed along with the patches applied before
https://git.busybox.net/buildroot/commit/package/libxml2?id=dc0e7cfc3e4050ce7c0404b11f747bf1500c50b7

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>