remove wxMSW-specific FindSuitableParent() and use GetParentForModalDialog() everywhere; extend it with additional checks and remove redundant ones elsewhere

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60559 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/os2/dialog.h

@@ -95,14 +95,6 @@ public:
 #endif // WXWIN_COMPATIBILITY_2_6
 
 protected:
-    //
-    // find the window to use as parent for this dialog if none has been
-    // specified explicitly by the user
-    //
-    // may return NULL
-    //
-    wxWindow *FindSuitableParent() const;
-
     //
     // Common part of all ctors
     //