Only in cases where you "inherit" from `base.json` and do not provide any `externs` member, you get the `externs` from `base.json`.  The `examples-all.json` config defines its own `externs` (and `inputs`) member.

So it is really not necessary to have any `externs` member at all in `base.json` given the way we currently use it.  I could remove this member altogether if you'd prefer.