Remove PVSS from lib_crypto and protocol environments

Context

An implementation of a PVSS (Publicly Verifiable Secret Sharing) scheme has been part of lib_crypto and available in protocol environments since V1, but has remained unused. With no plans to use it in the future either, we propose removing it altogether.

Manually testing the MR

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