Do not create Associtions in CompanionDeviceDiscoveryService

Since and T Associations objects will have the ID feilds. These IDs
must be unique, and will be assigned by the CdmService. To make this
possible all new Associations objects (records) should be created by the
CdmService. At the moment, however, CompanionDeviceDiscoveryService also
creates Associations objects.
Change ICompanionDeviceDiscoveryService interface, so that when it
discovers a device reports back to the CdmService only the mac address
of the device, instead of a fully constructed Association object.
CdmService will take the address and creates an Association itself.

Bug: 197933995
Test: make
Change-Id: I4af928a7bc1c690bc7c3c7c50ec896884e10e3bd