Remove RemoteService RPC's
Gitaly currently has RPC's that let the client set Git remotes in a repository: AddRemote, RemoveRemote, ListRemotes. I propose that we work towards removing these RPC's.
Of these three, AddRemote is used the most, immediately followed by FetchRemote. We are already working towards a solution, namely to embed the remote URL into FetchRemote via the remote_params field.
This will also help Gitaly HA because it means we won't have to "replicate" the existence / value of a Git remote.