Remove the unused variable introduced by 19c1b90e.

Fixes: 19c1b90e ("af_vsock: separate receive data loop")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>