Revert updates to cid/multihash

[Stebalien]

Unfortunately, updating cid & mutlihash breaks pretty much everything:

• The FFI imports two versions of the FVM which now use two different CID/Multihash versions.
• We have a common blockstore trait that uses CID in the interface.
• This will likely cause hell for builtin actors.

We can un-revert this if we can backport the changes. But we're not updating cid and/or multihash for the foreseeable future.

[Stebalien]

If someone wants to make this happen, they'll need to either:

1. Create patch releases of cid/multihash.
2. Add an abstraction to the filecoin-ffi to handle translating CIDs and the blockstore.

But I really don't have time for that right now.

[Stebalien]

@lemmih I'm really sorry about this. If you can find another way, I'd love to hear it.

[lemmih]

@lemmih I'm really sorry about this. If you can find another way, I'd love to hear it.

Can't we just bump the CID dependency everywhere?

[lemmih]

@lemmih I'm really sorry about this. If you can find another way, I'd love to hear it.

filecoin-ffi already deals with difference versions of all the shared types. It having to deal with different versions of cid only seems fitting.

[vmx]

As it's kind of related. There was another breaking rust-multihash release yesterday and there will be a breaking rust-cid release soon.

[lemmih]

@Stebalien Given that fvm doesn't follow semantic versioning, how about we bump to cid-0.9 and release a new version of fvm-2?