Fix comments for Grumpkin curve generator

[Pratyush]

Description

Fixes incorrect docs for Grumpkin

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• Targeted PR against correct branch (master)
• Linked to Github issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

[CPerezz]

I see what happened finally.
The halo2curves docs point to https://github.com/privacy-scaling-explorations/halo2curves/blob/6e2ff3853c8fe91300650a733100640dacf313e6/src/grumpkin/curve.rs#L43 a commit specifically which contains the wrong docs.

Therefore, in the latest master, this was already fixed in barretenberg. See: AztecProtocol/barretenberg@f2eca7d

Apologies for the inconvenience and the doc nits @Pratyush 🙏

[CPerezz]

Added a relevant changelog entry to the Pending section in CHANGELOG.md

Wasn't done. Should I do a PR for it?

[Pratyush]

I can add it to this PR!