netdev-dpdk: Remove dpdkvhostcuse ports

netdev-dpdk: Remove dpdkvhostcuse ports

This commit removes the 'dpdkvhostcuse' port type from the userspace
datapath. vhost-cuse ports are quickly becoming obsolete as the
vhost-user port type begins to support a greater feature-set thanks to
the addition of things like vhost-user multiqueue and potential
upcoming features like vhost-user client-mode and vhost-user reconnect.
The feature is also expected to be removed from DPDK soon.

One potential drawback of the removal of this support is that a
userspace vHost port type is not available in OVS for use with older
versions of QEMU (pre v2.2). Considering v2.2 is nearly two years old
this should however be a low impact change.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>