don't use annoying and unneeded in C++ casts of NULL to "T *" in all other files neither

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58227 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/bitmap.h

@@ -85,7 +85,7 @@ public:
     wxBitmap GetSubBitmap( const wxRect& rect ) const;
 
     bool SaveFile(const wxString &name, wxBitmapType type,
-                          const wxPalette *palette = (wxPalette *)NULL) const;
+                          const wxPalette *palette = NULL) const;
     bool LoadFile(const wxString &name, wxBitmapType type = wxBITMAP_DEFAULT_TYPE);
 
 #if wxUSE_PALETTE