We do not need CLASS_DEF for things we do not write

We do not need CLASS_DEF for things we do not write, and for the things we want it, it should be un-versioned

Ping @akraszna as he spotted it .

Anyhow I had assumed these were all "cleaned" very early on i.e around 2014

Our "current" git history for e/gamma seems to start from -81 below

2014-09-07  RD Schaffer  <R.D.Schaffer@cern.ch>
0401 
0402         * tagging as xAODEgamma-00-00-81
0403         * removing CLASS_DEF from Electron.h and Photon.h
0404 
0405 2014-09-04  RD Schaffer  <R.D.Schaffer@cern.ch>
0406 
0407         * tagging as xAODEgamma-00-00-80
0408         * xAODEgamma/ElectronAuxContainer.h: moved all CLASS_DEF to the
0409         unversioned class files