fix de-registration of non-free extensions

[rjschwei]

#208 introduced

suseconnect = run_SUSEConnect(
                    registration_target=get_current_smt(),
                    product=triplet,
                    de_register=True
              )

However, this will fail on a transactional-update system. While the run_SUSEConnect function uses the proper command, i.e. transactional-update instead of SUSEConnect the transactional-update command does not have a deregister option. We should create a feature request for such an option and this issue becomes moot.

At this moment this is not an issue as we do not have LTSS for SL-Micro. However, the requirements doc for SLES 16 For SAP includes a transaction-update setup and SLES For SAP will eventually have LTSS support. As such this needs to be addressed to also support deregistration via transactional-update