Make Gitlab::Git::GitlabProjects not work with storage paths

Gitlab Shell's command gitlab-projects has been moved into Gitlab::Git https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15853 🎉

Currently it has the following initializer params: shard_path, repository_relative_path, global_hooks_path:, logger:. This dependency on shard paths makes it unfit for the post-gitaly world. We should adapt this code to fix this.

/cc @gl-gitaly because this will impact several endpoints.