gtk3: Remove scrollbars

Under GTK3, the scrollbars fade in and out, causing a cascade of
re-paint events.  These cause KiCad to be unresponsive while the repaint
events occur.  By default this is 1s fade in 1s fade out but can be
configured by the user/wm.

Area mapping the repaint events to just scrollbar areas will be a good
solution but until/unless that happens the scrollbars in GTK3 are
problematic.

common/draw_panel_gal.cpp

@@ -72,7 +72,13 @@ EDA_DRAW_PANEL_GAL::EDA_DRAW_PANEL_GAL( wxWindow* aParentWindow, wxWindowID aWin
     SwitchBackend( aGalType );
     SetBackgroundStyle( wxBG_STYLE_CUSTOM );
 
+#ifdef __WXGTK3__
+    // Until we can handle the repaint events from scroll bar hide/show
+    // todo: Implement area mapping for re-painting scrollbars
+    ShowScrollbars( wxSHOW_SB_NEVER, wxSHOW_SB_NEVER );
+#else
     ShowScrollbars( wxSHOW_SB_ALWAYS, wxSHOW_SB_ALWAYS );
+#endif
     EnableScrolling( false, false );    // otherwise Zoom Auto disables GAL canvas
 
     Connect( wxEVT_SIZE, wxSizeEventHandler( EDA_DRAW_PANEL_GAL::onSize ), NULL, this );

common/view/wx_view_controls.cpp

@@ -602,6 +602,12 @@ wxPoint WX_VIEW_CONTROLS::getMouseScreenPosition() const
 
 void WX_VIEW_CONTROLS::UpdateScrollbars()
 {
+#ifdef __WXGTK3__
+    // Until we can handle the repaint events from scroll bar hide/show
+    // todo: Implement area mapping for re-painting scrollbars
+    return;
+#endif
+
     const BOX2D viewport = m_view->GetViewport();
     const BOX2D& boundary = m_view->GetBoundary();