Offboards a compute VPC to be NSX unmanaged from a transit VPC.
All the VMs in the compute VPC need to be untagged before offboarding
the compute VPC. Offboarding status can be obtained from
/csm/aws/compute-vpcs//status API. Upon successful offboarding
compute VPC, the onboard_step will be OFFBOARD_SUCCESSFUL
and op_status will be NOT_AVAILABLE. If any error is encountered
during offboarding, corresponding error_code and error_message
will be populated.