vdpa_sim: remove unnecessary headers inclusion

Some headers are not necessary, so let's remove them to do
some cleaning.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20201215144256.155342-3-sgarzare@redhat.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>