[univalue] Lint the univalue code
Summary: Now that we maintain our own version and that we are in sync with core master, it's time to properly format the code with our linter suite.
Test Plan:
ninja all check-univalue arc lint
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D16308