The branches mongodb-4.0 and mongodb-3.6 are now obsolete as the corresponding MDB release series have been EOL, we could remove wherever we reference them.

So far I found that we reference them in evergreen.yml and  compatibility_test_for_releases.sh and import_compatibility_test.sh.

Note: The use of mongodb-4.0 in the compatibility tests is still important for customers who move from 4.0 to 4.2, hence we don't want to remove the references of mongodb-4.0 in this script.