For future merging
Use system univalue by default
Previous discussion was in #7349, where it was decided not to automatically use an installed univalue in favor of the included one.
Why would you opt for system default? Out of interest.
Standard best practices. Libraries shouldn't be bundled at all. We have a reasonable case for bundling consensus-critical ones like LevelDB and libsecp256k1, but Univalue is not consensus-critical at all.
We're not going to do this (at least for the forseeable future), so closing for now.