unit: Remove leftover unregister test cases
unit: Remove leftover unregister test cases

Malformed PDUs are not accepted by knotd service. No response is
sent reporting protocol error.

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source