Comment two declarations which have no implementation
Improve fix for ROOT-5627

Re-align the genreflex and rootcling tools, removing specialities.
Delegate to the scanner the responsability to mark the
AnnotatedRecordDecl instances as needing the streamer info if
the selction file is an xml one.
The functionality of producing "old stremers" for legacy reasons is
left to rootcling and linkDef files.