Removing incompatible ART tests from 21.0

Hi,

this MR removes muon ART tests which are not runnable in 21.0.

test_checkgeo_agdd.sh
test_checkgeo_amdc.sh
test_checkgeo_nswd.sh
test_gengeo_agdd.sh
test_gengeo_amdc.sh
test_gengeo_nswd.sh

are testing the AmdcAth package which does not exist in 21.0. Thus, the tests can never succeed.

test_nsw_singlemuon_digit.sh
test_nsw_singlemuon_evntgen.sh

are testing simulation of (outdated) Run 3 layouts (including NSWs). 21.0 is not compatible with processing NSW layouts since it diverged from 21.3/master by a lot. Thus, those tests are not useful anymore.

Best, Nico