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.
To simplify migration from 1.0 to 1.1, do not allow data classes to
automatically implement abstract equals/hashCode/toString declared in
super-interfaces (KT-11306) if "-language-version 1.0" is specified
