Method Class_Version() must be both 'static' and 'public'

genreflex is producing at least two errors while compiling CMSSW
with

    method Class_Version() must be both 'static' and 'public'.

for class reco::LeafRefCandidateT.

Move Class_Version() from protected to public to meet Reflex
requirements.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #5687 from davidlt/fix-reflex-reco-errors

Method Class_Version() must be both 'static' and 'public'