Clean up un-needed TRTPreProcessingCfg for TRTExtension config

Thomas Streblerrequested to merge
tstreble/athena:TRTPreProcClean into main

TRTPreProcessingCfg is already scheduled in https://gitlab.cern.ch/atlas/athena/-/blob/main/InnerDetector/InDetConfig/python/TrackRecoConfig.py?ref_type=heads#L175

Removing it from the TRTExtension configs

FYI @fatsai

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