vhost: remove unused function prototype
vhost: remove unused function prototype

vhost_user_host_notifier_ctrl is not existed anymore, its statement in
header file should be removed accordingly.

Fixes: 43f34e35663f ("vhost: provide helper for host notifier ctrl")

Signed-off-by: Xiaolong Ye <c7d6fc2f7e22da80deb234d523238b510a8c0f08@intel.com>
Reviewed-by: Tiwei Bie <f338cf29d7d69ff1bc99f755ebfb0eb0accd409e@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk