Scoru,Proto: deprecate [cement] parameter from [Smart_rollup_cement]

Context

The protocol computes the unique commitment (if it exists), and checks if it matches the provided one. We can remove this from the operation and only mention in the receipt the cemented commitment. The field is for now deprecated and can be removed in the next protocol.

Manually testing the MR

Existing tests should be ok?

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