Clean up orchestration test scripts

continuousintegration/orchestration/tests directory contains a set of bash and python scripts. EOSCTA documentaion proposes to use some of these script for testing of a CTA instance after the buildtree installation. CI also calls them for the tests.

However, some of the scripts seem to be outdated (use non-existent cta commands) or not used at all. Among those:

• migration.sh - not mentioned in migration section, is it used?
• grpc_dir_inject.sh (called only from migration.sh)
• multiple_repack_wrapper.sh - not mentioned in repack section, is it used? CI runs repack_systemtest_wrapper.sh but not these ones.
• multiple_repack.sh (called only from multiple_repack_wrapper.sh)
• simple_repack.sh
• simpletest.cli.sh - uses outdated kubectl exec ctacli -- cta instead of kubectl exec ctacli -- cta-admin
• simpletest.mgm.sh
• systest.sh - cta instead of cta-admin
• systest_xrdcp_many_concurrent_files.sh - cta instead of cta-admin
• systest_xrdcp_many_files.sh - cta instead of cta-admin

I suspect migration and repack scripts might be used occasionally, but grep hasn't found anything in the docs. Please review this list and identify the files that are not needed.