storage: GitStateManager.WriteState tidy-up.
storage: GitStateManager.WriteState tidy-up.

- Less indentation.
- Shorter-scoped variables.
- Remove named err error output.

samsalisbury/sous,opentable/sous,opentable/sous,opentable/sous,samsalisbury/sous,opentable/sous,samsalisbury/sous,samsalisbury/sous,opentable/sous,samsalisbury/sous