Stop stubbing StubUserLang
Stub objects are confusing as heck and are a performance optimization
that really aren't fit for the modern era. They were designed to avoid
loading the actual code from the disk back in the days when bytecode
caching wasn't always gonna be there.
It's 2017. If you're using HHVM, you've got a bytecode cache. If you're
using any reasonably recent version of PHP then you've got the opcode
caching enabled by default in basically every distro-related build.
Nothing actually relies on this object being a stub (that'd be silly),
so only references are basically things force unstubbing (also kind of
silly) the object. Once remaining code referencing this in extensions
are all cleaned up then we can remove the class itself.