Piano: Remove waveform cycling with C

This is not the most useful keyboard binding anyways, plus it will be
extremely hacky to implement it with the generic processor parameter
widgets. Therefore, we'll get rid of it and add back a more generic
keyboard binding system later.

Userland/Applications/Piano/KnobsWidget.cpp

@@ -104,11 +104,6 @@ KnobsWidget::KnobsWidget(TrackManager& track_manager, MainWidget& main_widget)
     }
 }
 
-void KnobsWidget::cycle_waveform()
-{
-    m_synth_waveform->set_selected_index((m_synth_waveform->selected_index() + 1) % m_synth_waveform->model()->row_count());
-}
-
 void KnobsWidget::update_knobs()
 {
     // FIXME: This is needed because when the slider is changed normally, we

Userland/Applications/Piano/KnobsWidget.h

@@ -26,7 +26,6 @@ public:
     virtual ~KnobsWidget() override = default;
 
     void update_knobs();
-    void cycle_waveform();
 
 private:
     KnobsWidget(TrackManager&, MainWidget&);

Userland/Applications/Piano/MainWidget.cpp

@@ -115,9 +115,6 @@ void MainWidget::special_key_action(int key_code)
     case Key_X:
         set_octave_and_ensure_note_change(DSP::Keyboard::Direction::Up);
         break;
-    case Key_C:
-        m_knobs_widget->cycle_waveform();
-        break;
     case Key_Space:
         m_player_widget->toggle_paused();
         break;