Remove unnecessary line...

... This is a vestige of the time when "Waveform" and "Waveform dB" were
considered separate wave track view types.  But now that scale choice is
independent of Waveform vs. Spectrogram choice, there is no possible change of
scale type happening here, requiring invalidation of the vertical ruler.

src/tracks/playabletrack/wavetrack/ui/WaveTrackControls.cpp

@@ -766,7 +766,6 @@ void WaveTrackMenuTable::OnSetDisplay(wxCommandEvent & event)
          !(displays.size() == 1 && displays[0].id == id);
       if (wrongType) {
          for (auto channel : TrackList::Channels(pTrack)) {
-            channel->SetLastScaleType();
             WaveTrackView::Get( *channel )
                .SetDisplay( WaveTrackView::Display{ id } );
          }