vmm, config, vhost_user_blk: remove "wce" parameter

This config option provided very little value and instead we now enable
this feature (which then lets the guest control the cache mode)
unconditionally.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/device_manager.rs

@@ -1336,7 +1336,7 @@ impl DeviceManager {
                 queue_size: disk_cfg.queue_size,
             };
             let vhost_user_block_device = Arc::new(Mutex::new(
-                vm_virtio::vhost_user::Blk::new(id.clone(), disk_cfg.wce, vu_cfg)
+                vm_virtio::vhost_user::Blk::new(id.clone(), vu_cfg)
                     .map_err(DeviceManagerError::CreateVhostUserBlk)?,
             ));