TheFirstPlaceLoser - removing unnecessary calls to `TransportFailed`

`ServerSentEventsTransport` and `LongPollingTransport` registered callbacks to let the `TransportInitializationHandler` know that the transport failed (by calling the `TransportFailed` method) when the `disconnectToken` is tripped . This was unnecessary since the `TransportInitializationHandler` registered first its own callback for the same reason which would call `TransportInitializationHandler.Fail()`. Because we use the `SafeThreadInvoker` for invoking the `Fail()` method the calls from the transport implementations were no-ops because they would have happened after the call from the `TransportInitializationHandler` which in turn would make `SafeThreadInvoker` ignore any further calls.