This is a small PR that cleans up compiler warnings.
The most controversial change is removing the `data_dir` field from the `BeaconChainBuilder`.
It was removed because it was never read.
Co-authored-by: Paul Hauner <paul@paulhauner.com>
Co-authored-by: Herman Junge <hermanjunge@protonmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>