TrkEventAthenaPool ROOT Dictionary Loading Fixes, master branch (2020.07.20.)

Removed some workarounds introduced for ROOT 6.20/02. Now with LCG_97a (ROOT 6.20/06, which apparently doesn't have a release page on https://root.cern. 😕) these workarounds/hacks were actually causing problems for the jobs. Like in:

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master/2020-07-18T2101/Athena/x86_64-centos7-gcc8-dbg/Athena/UT/TrkEventAthenaPool.log.html

Without them, the jobs can run successfully though.

Pinging @ssnyder.