Remove using declarations in root-cling dictionary files to avoid interpreter clashes with the global namespace

This variable was previously not exported, and the corresponding relaxed python version check was not executed because of this.
This means DD4HEP_RELAX_PYVER was functional in the DD4hep build itself, but not in downstream builds.

The [TGeoTrap class](https://root.cern.ch/doc/master/classTGeoTrap.html#a0e27ff95f2ffa2eb8c320a7778e1f403) (for which an object is created here) has a slightly different calling syntax than what is done internally in [G4Trap](https://apc.u-paris.fr/~franco/g4doxy/html/classG4Trap.html#074ca31710e0a11f9c7b6b13ddd1eabf). We need to take the atan here to get to the angle that TGeoTrap wants.

Remove using declarations in root-cling dictionary files to avoid interpreter clashes with the global namespace

Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Use of nicely named variables such as $p may clash with local user
environments. A similar change was implemented in ROOT a long time
ago:
https://github.com/root-project/root/commit/bba80a143655a4aac63cb5adb2e9f2d73bcd9566