Remove unused declarations from Viewport.h
diff --git a/vncviewer/Viewport.h b/vncviewer/Viewport.h
index f73a27d..b50c815 100644
--- a/vncviewer/Viewport.h
+++ b/vncviewer/Viewport.h
@@ -22,15 +22,11 @@
 
 #include <map>
 
-namespace rfb { class ModifiablePixelBuffer; }
-
 #include <FL/Fl_Widget.H>
 
 class Fl_Menu_Button;
 class Fl_RGB_Image;
 
-namespace rfb { class PixelTransformer; }
-
 class CConn;
 class PlatformPixelBuffer;