MAINTAINERS: Remove IP MASQUERADING record

This entry is in MAINTAINERS for historical purpose.
It doesn't match current sources since the commit
adf82acc ("netfilter: x_tables: merge ip and
ipv6 masquerade modules") moved the module.
The net/netfilter/xt_MASQUERADE.c module is already under
the netfilter section. Thus, there is no purpose to keep this
separate entry in MAINTAINERS.

Cc: Florian Westphal <fw@strlen.de>
Cc: Juanjo Ciarlante <jjciarla@raiz.uncu.edu.ar>
Cc: netfilter-devel@vger.kernel.org
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>