Revert a02bbb1c: MAINTAINERS: add virtio-dev ML for virtio

The OASIS virtio-dev mailing list is a good place for implementers to
discuss details of the standard, but it requires subscription to avoid
IP issues :(

It makes more sense to stick with the
virtualization@lists.linux-foundation.org mailing list for bug
reports.  We can refer to the OASIS list if it involves a question on
the standard itself.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>