Remove compile-time checks for always defined WM_XXX in wxMSW

The symbols in question are present at least since XP, and most of them since
Windows 2000, so remove preprocessor checks for them, they shouldn't be needed
when any remotely current compiler/SDK.

src/msw/listctrl.cpp

@@ -3157,12 +3157,10 @@ wxListCtrl::MSWWindowProc(WXUINT nMsg, WXWPARAM wParam, WXLPARAM lParam)
 {
     switch ( nMsg )
     {
-#ifdef WM_PRINT
         case WM_PRINT:
             // we should bypass our own WM_PRINT handling as we don't handle
             // PRF_CHILDREN flag, so leave it to the native control itself
             return MSWDefWindowProc(nMsg, wParam, lParam);
-#endif // WM_PRINT
 
         case WM_CONTEXTMENU:
             // because this message is propagated upwards the child-parent