virtio-devices: vhost_user: remove unused restore_backend_connection

This function hasn't been used since '22.
All callers removed with:
1f0e5eb66 vmm: virtio-devices: Restore every VirtioDevice upon creation

TEST: build and cargo test all still pass, grep returns no results.

Signed-off-by: Dylan Reid <dgreid@fb.com>

virtio-devices/src/vhost_user/mod.rs

@@ -528,22 +528,6 @@ impl VhostUserCommon {
         })
     }
 
-    pub fn restore_backend_connection(&mut self, acked_features: u64) -> Result<()> {
-        let mut vu = VhostUserHandle::connect_vhost_user(
-            self.server,
-            &self.socket_path,
-            self.vu_num_queues as u64,
-            false,
-            None,
-        )?;
-
-        vu.set_protocol_features_vhost_user(acked_features, self.acked_protocol_features)?;
-
-        self.vu = Some(Arc::new(Mutex::new(vu)));
-
-        Ok(())
-    }
-
     pub fn reset(&mut self, id: &str) {
         // Resume the virtio thread if it was paused. Reset must always
         // converge to fresh state, so backend resume / reset failures are