Backporting univalue. Also fix broken test data from previous commit.
Summary: Backport latest univalue version to fix minor bugs and cleanup namespaces. This change also fixes the test data that broke from the previously reverted change.
Test Plan: Tests pass (now).
Reviewers: deadalnix, O1 Bitcoin ABC, #bitcoin_abc
Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D739