Inherit all wxList ctors in wxResourceCache

Simplify this deprecated class a bit to avoid explicitly mentioning
wxList ctor which will soon be itself deprecated too.

include/wx/gdicmn.h

@@ -986,10 +986,7 @@ wxDEPRECATED_MSG("Use wxList directly or just a standard container")
 wxResourceCache : public wxList
 {
 public:
-    wxResourceCache() = default;
-#if !wxUSE_STD_CONTAINERS
-    wxResourceCache(unsigned int keyType) : wxList(keyType) { }
-#endif
+    using wxList::wxList;
     virtual ~wxResourceCache()
     {
         wxList::compatibility_iterator node = GetFirst ();