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.
Synthesized 'copy' introduces default values for parameters, which is
prohibited for regular overrides.
Report warning in language version 1.2-, error in 1.3+.
Alexander Udalov