Remove LANGUAGE_VERSION from non-coroutine codegen tests

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.

compiler/testData/codegen/box/enum/deepInnerClassInEnumEntryClass.kt

@@ -1,5 +1,4 @@
 // IGNORE_BACKEND: JVM_IR
-// LANGUAGE_VERSION: 1.2
 
 enum class A {
     X {
@@ -22,4 +21,4 @@ enum class A {
     abstract val test: String
 }
 
-fun box() = A.X.test
+fun box() = A.X.test