Clarified comments around the JUCE_ALLOW_STATIC_NULL_VARIABLES items to make clear that they're deprecated

modules/juce_gui_basics/juce_gui_basics.h

@@ -117,8 +117,6 @@ namespace juce
     class MouseInputSource;
     class MouseInputSourceInternal;
     class ComponentPeer;
-    class MarkerList;
-    class RelativeRectangle;
     class MouseEvent;
     struct MouseWheelDetails;
     struct PenDetails;
@@ -130,28 +128,21 @@ namespace juce
     class ComboBox;
     class Button;
     class FilenameComponent;
-    class DocumentWindow;
     class ResizableWindow;
-    class GroupComponent;
     class MenuBarComponent;
-    class DropShadower;
     class GlyphArrangement;
-    class PropertyComponent;
     class TableHeaderComponent;
     class Toolbar;
-    class ToolbarItemComponent;
     class PopupMenu;
     class ProgressBar;
     class FileBrowserComponent;
     class DirectoryContentsDisplayComponent;
     class FilePreviewComponent;
-    class ImageButton;
     class CallOutBox;
     class Drawable;
     class DrawablePath;
     class DrawableComposite;
     class CaretComponent;
-    class BubbleComponent;
     class KeyPressMappingSet;
     class ApplicationCommandManagerListener;
     class DrawableButton;