Remove the legacy DBus control interface

[amboar]

With expanded use of DBus to implement alternative transports, an alternative and more ergonomic control interface was exposed on DBus. The old interface is considered deprecated; mboxctl already uses the new interface and the old interface can be removed as of the submission of https://gerrit.openbmc-project.xyz/#/c/openbmc/openpower-pnor-code-mgmt/+/19246/