Remove transport dir name from TransportClient

To be able to re-use the TransportClient infra for transport
registration, I need to remove transport dir name property from
TransportClient because it's not available before registration
itself. As a result callsites that used getTransportDirName()
from TransportClient will have to go through the
TransportManager for that. Bryan suggested that the
TransportClient wasn't the best place for the property before.

Ref: http://go/br-binding-on-demand
Bug: 17140907
Test: m -j RunFrameworksServicesTests
Change-Id: I3fa335faf97d63adfad1a929336073a70fc8bc02