Now that we're keeping track of transfer digests, initializing any on-
chain state through the `InstantiateMsg` doesn't make a lot of sense:
any state initialized this way is unverified and this message doesn't
contain enough information to generate the transfer digests.
Rather than trying to add in the necessary fields, just drop the message
completely since it won't be used in production. It's currently only
used to initialize on-chain state for tests but the same thing can be
accomplished through the `ModifyBalance` and `SubmitVAAs` methods.
Add support for handling chain registration VAAs for the tokenbridge
contract. This will let us deploy accounting without also having to
deploy the tokenbridge.
Chirantan Ekbote