fsck: Avoid complaining about required content of dead repositories

fsck: Avoid complaining about required content of dead repositories

requiredContentMap does not exclude dead repos. Usually this is not a
problem because it is used when we are operating on a repository, and in
that case, the repository is not dead (or if it is, the required content
configurations should still be used). But in the case of fsck, this made a
old required content config for a dead repository be warned about in a
situation where it is not a problem.