Make _moveDelegateVotes internal in Votes.sol

[ernestognw]

🧐 Motivation

A question came in the forum regarding customizing the quorum of a Governor so that it takes the amount of delegated votes into account. This use case is already possible by tracking the total of delegate votes through both the _transferVotingUnits and _delegate functions but it's unnecessarily expensive and it splits the logic in two when it can already be tracked by overriding _moveDelegateVotes.

Reference

📝 Details

Making _moveDelegatesVotes internal enables overriding.

[ernestognw]

Closing in favor of #4989