[IO] Deprecate TStreamerElement::ESTLtype in favor of ROOT::ESTLType

Author: eguiraud

core/meta/inc/TStreamerElement.h

@@ -55,7 +55,7 @@ class TStreamerElement : public TNamed {
 
 public:
 
-   enum ESTLtype {
+   enum R__DEPRECATED(6, 26, "Please use ROOT::ESTLType instead.") ESTLtype {
       kSTL                  = ROOT::kSTLany,
       kSTLstring            = ROOT::kSTLstring,
       kSTLvector            = ROOT::kSTLvector,