Remove SharedLog usage from NetworkStackClient

As was pointed out, SharedLog in NetworkStackClient (and
ConnectivityModuleConnector) was only used for dump() functionality
which is not called by anyone. This CL removes the unused dump()
functions and removes SharedLog usage in favor of android.util.Log.

Also cleaning up usage of Slog so only logWtf logs to the system log in
both NetworkStackClient and ConnectivityModuleConnector.

Test: m
Bug: 235901424
Change-Id: Ia484ee825cd714fd8eb7704ca1d16acfbe2e7331