Avoid hashing payload before signing (#1391)

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including relevant motivation and context.

# Checklist:
Remove the checklist to signal you've completed it. Enable auto-merge if
the PR is ready to merge.
- [x] If the pull request requires a cryptography review (e.g.
cryptographic algorithm implementations) I have added the 'crypto' tag.
- [x] I have reviewed my diff in github, line by line and removed
unexpected formatting changes, testing logs, or commented-out code.
- [x] Every change is related to the PR description.
- [x] I have
[linked](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue)
this pull request to relevant issues (if any exist).

yarn-project/noir-libs/noir-aztec/src/constants_gen.nr

@@ -101,6 +101,7 @@ global GENERATOR_INDEX__SIGNED_TX_REQUEST = 25;
 global GENERATOR_INDEX__GLOBAL_VARIABLES = 26;
 global GENERATOR_INDEX__PARTIAL_CONTRACT_ADDRESS = 27;
 global GENERATOR_INDEX__TX_REQUEST = 33;
+global GENERATOR_INDEX__SIGNATURE_PAYLOAD = 34;
 global GENERATOR_INDEX__VK = 41;
 global GENERATOR_INDEX__PRIVATE_CIRCUIT_PUBLIC_INPUTS = 42;
 global GENERATOR_INDEX__PUBLIC_CIRCUIT_PUBLIC_INPUTS = 43;