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/gtk/dirdlg.h

@@ -37,9 +37,7 @@ public:
 
 public:     // overrides from wxGenericDirDialog
 
-    wxString GetPath() const wxOVERRIDE;
     void SetPath(const wxString& path) wxOVERRIDE;
-    void GetPaths(wxArrayString& paths) const wxOVERRIDE;
 
 
     // Implementation only.
@@ -56,8 +54,6 @@ protected:
 
 
 private:
-    wxArrayString m_paths;
-
     wxDECLARE_DYNAMIC_CLASS(wxDirDialog);
 };