Most of these tests used this directive as a way to opt in to a new
language feature, and most of those features are already stable for a
long time, so no opt-in is needed. Some other tests used the directive
to opt out from a language feature, replace those by the `LANGUAGE`
directive. One test used the directive to test behavior that actually
depended on the API version; use `API_VERSION` directive there instead.
Constant expressions are inlined if they do not depend on non-inlineable
vals.
Java constants are always inlined.
Kotlin constants are inlined in LV 1.1+.
