TCT: removing unneeded tests
This MR removes TCT tests which are not needed:
- test_MC_Run2Reprocessing.sh - same test is present elsewhere: https://gitlab.cern.ch/atlas/athena/blob/master/Tools/TrfTestsART/test/test_trf_mcoverlay_mc20e_fullchain_mt.sh
- test_mainstream_run276689_collisions and test_mainstream_run307716_collisions - use outdated settings
Tagging @rmazini