Remove unused test scripts in the CI

ReleaseNotes.md

continuousintegration/orchestration/tests/grpc_dir_inject.sh

continuousintegration/orchestration/tests/migration.sh

continuousintegration/orchestration/tests/multiple_repack.sh

...ntegration/orchestration/tests/multiple_repack_wrapper.sh

continuousintegration/orchestration/tests/simple_repack.sh

continuousintegration/orchestration/tests/simpletest.cli.sh

continuousintegration/orchestration/tests/simpletest.mgm.sh

continuousintegration/orchestration/tests/systest.sh

...rchestration/tests/systest_xrdcp_many_concurrent_files.sh

...tegration/orchestration/tests/systest_xrdcp_many_files.sh