Proto: Fix incorrect comment

Context

I have come across an incorrect comment in the Tezos protocol. The original comment assumed the Kind module is re-exported here. Yet, that Kind module is contained inside the Lazy_storage module.

The actual definition comes from Operation_repr.Kind, which is included in Alpha_context here.

Manually testing the MR

CI

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR