vhost: remove vhost-cuse

vhost: remove vhost-cuse

remove vhost-cuse code, including the eventfd_link kernel module that
is for vhost-cuse only.

The lib/virt/qemu-wrap.py is also removed, as it's mainly for vhost-cuse
usage.

As we have one vhost implementation now, one vhost config option is
needed only. Thus, CONFIG_RTE_LIBRTE_VHOST_USER is removed.

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>