Currently version_gen is a bottleneck in our build that sometimes takes a long time to provision, and takes over a minute for a script that takes less than a second. This script was initially added as https://jira.mongodb.org/browse/SERVER-63191 to prevent a race condition causing us to version binaries improperly for release. While we should leave it on in nightly to continue to prevent that race condition, we don't need as strict a method for mongo-master.