Remove the Cbor trait and impl from all param/return types

[anorth]

The Cbor trait has a couple of convenience functions that become made available as methods on types implementing it. Only one of these is used at all (marshal_cbor) and it only a couple of times. It's not worth the noise.

Remove the trait and change the couple of uses of it to use existing serialize() functions.

[arajasek]

@anorth The Cbor trait is currently used by the entirety of the integration test suite (see here). Do you have an easy way in mind to refactor around this?

If not, I'd rather close this issue -- strikes me as a lot of work for not much gain.

[anorth]

Yes I think we should just do the work, though it's quite annoying that we have to do that work in FVM first.

[arajasek]

@anorth Okay, I'm gonna get to this sooner rather than later then, maybe as part of filecoin-project/ref-fvm#987.

I don't want to wait longer, because actors currently cannot update to the latest Helix FRC-0046 library since the change has already landed there, and I'm uncomfortable being in that position.

[vyzo]

Why are we making work for ourselves?

[anorth]

actors currently cannot update to the latest Helix FRC-0046 library

Thanks, I see this as yet more support for removing it. If a library providing some param/return types merely forgot to add the Cbor impl we'd have to go through a whole third-party repo release cycle to fix it. The coupling is terrible.

I had also added this to my TODO list. Please call on me for any support.

[anorth]

The Cbor trait is still used in the test VM. This issue title doesn't mention that, but the intention is to drop it entirely.