SERVER-42520, Bernard Gorman created a CryptDReplicationCoordinatorNoOp class with empty implementations of all the ReplicationCoordinator interface methods. This code is part of mongocryptd in the enterprise repo.
SERVER-41882 and related code cleanups we're actively changing the ReplicationCoordinator interface, and I expect we'll continue to change it. Changes are inconvenient, however, because every change must be coordinated across the community and enterprise repos.
Let's move CryptDReplicationCoordinatorNoOp into the community code base and rename it ReplicationCoordinatorNoOp, so we can change it in sync with ReplicationCoordinator. Code in the enterprise module can still use the NoOp class (only for instantiating it), but changes in that class won't affect the enterprise code, since it doesn't explicitly call any of its methods.