Avoid overriding wxDirDialog::GetPath[s]() unnecessarily

Don't duplicate practically the same code in all ports, just add m_paths
itself to the base class. The only drawback of doing this is that it's
unused in the ports not (yet) using it, but this saves enough code in
the aggregate to be worth it.

include/wx/osx/dirdlg.h

@@ -51,10 +51,6 @@ public:
     // only for compatibility with older versions
     virtual void SetTitle(const wxString& title) wxOVERRIDE;
 
-    virtual wxString GetPath() const wxOVERRIDE;
-    virtual void GetPaths(wxArrayString& paths) const wxOVERRIDE;
-
-
 #if wxOSX_USE_COCOA
     virtual void ShowWindowModal() wxOVERRIDE;
     virtual void ModalFinishedCallback(void* panel, int returnCode) wxOVERRIDE;
@@ -72,7 +68,6 @@ private:
     // Common part of all ctors.
     void Init();
 
-    wxArrayString m_paths;
     wxString m_title;
 
     wxDECLARE_DYNAMIC_CLASS(wxDirDialog);