kbfsgit: don't use Unmarshal for the config storer
kbfsgit: don't use Unmarshal for the config storer

That's where the gcfg bug happens.  Instead do a manual deep copy,
including the unsupported fields.

Issue: KBFS-2353

keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client