refactor: cleanups post unsubtree'ing univalue

Mostly changes to remove src/univalue exceptions from the various linters,
and the required code changes to make them happy. As well as minor doc
changes.

.gitignore

@@ -44,8 +44,6 @@ src/obj
 share/setup.nsi
 share/qt/Info.plist
 
-src/univalue/gen
-
 src/qt/*.moc
 src/qt/moc_*.cpp
 src/qt/forms/ui_*.h