R1:8d087ae738d8

Remove 'initFromConduit' option from Diffusion

Summary:
Ref T2783. I think this served two purposes:

- Improving performance in cases where we "know" a repository is local.
- Preventing loops.

It is now obsolete:

- After D11476, refs can almost always resolve on a fast path.
- As T2783 moves forward, we can usually no longer know when a repository is local without actually looking it up -- almost everything is allowed to run anywhere.
- The cluster behavior in D11475 now prevents loops.

Test…