Remove onError() and onCompleted() callback from UtpTestResultListener

onError() and onCompleted() is an internal state of gRPC connection
which should not be exposed directly in UtpTestResultListener.
When error happened, UtpTestResultListener.onTestResultEvent() is
called with test result status ERROR.

Bug: n/a
Test: UtpTestResultListenerServerTest and UtpConnectedTest
Change-Id: If5da0b3729fb8a28c47cf56a05da2636a9657639
4 files changed