MAINTAINERS: Remove mailing-list entry for XDP (eXpress Data Path)

This removes the mailing list xdp-newbies@vger.kernel.org from the XDP
kernel maintainers entry.

Being in the kernel MAINTAINERS file successfully caused the list to
receive kbuild bot warnings, syzbot reports and sometimes developer
patches. The level of details in these messages, doesn't match the
target audience of the XDP-newbies list. This is based on a survey on
the mailing list, where 73% voted for removal from MAINTAINERS file.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>