Kibosh the NrState Strings

The toString() method of NetworkRegistrationInfo and
ServiceState are being abused to get info that apps
really should be using: becuase the info can be misleading.

Instead, callers should use ServiceState#getCellBandwidths() and
or the onLinkDownstreamBandwidthKbps() methods from Connectivity
that are part of LinkProperties.

Bug: 172999992
Test: wip
Change-Id: Id4658acd30a50b35d55456ecca19bd92319eeba5