Time track properly warps the MIDI event times (but not pitches)

mMidiPlaySpeed doesn't handle all of the options provided by time tracks,
and in fact doesn't even use time tracks.  Using the time track
instead allows note tracks to remain synchronized with the rest of the audio.

mMidiPlaySpeed _did_ work where it was used in the transcription tool
bar, but that already updates a time track so no special handling is
needed.

src/toolbars/TranscriptionToolBar.cpp

@@ -475,9 +475,6 @@ void TranscriptionToolBar::PlayAtSpeed(bool looped, bool cutPreview)
    // Start playing
    if (playRegionStart >= 0) {
 //      playRegionEnd = playRegionStart + (playRegionEnd-playRegionStart)* 100.0/mPlaySpeed;
-#ifdef EXPERIMENTAL_MIDI_OUT
-      gAudioIO->SetMidiPlaySpeed(mPlaySpeed);
-#endif
       AudioIOStartStreamOptions options(p->GetDefaultPlayOptions());
       options.playLooped = looped;
       options.timeTrack = mTimeTrack.get();