Remove experimental coroutines support. Part 2

compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt

@@ -457,7 +457,7 @@ class DescriptorSerializer private constructor(
     }
 
     private fun MutableVersionRequirementTable.writeVersionRequirementDependingOnCoroutinesVersion(): Int =
-        writeVersionRequirement(if (extension.releaseCoroutines()) LanguageFeature.ReleaseCoroutines else LanguageFeature.Coroutines)
+        writeVersionRequirement(LanguageFeature.ReleaseCoroutines)
 
     private fun CallableMemberDescriptor.isSuspendOrHasSuspendTypesInSignature(): Boolean {
         if (this is FunctionDescriptor && isSuspend) return true

compiler/serialization/src/org/jetbrains/kotlin/serialization/SerializerExtension.kt

@@ -92,6 +92,4 @@ abstract class SerializerExtension {
     open fun serializeErrorType(type: KotlinType, builder: ProtoBuf.Type.Builder) {
         throw IllegalStateException("Cannot serialize error type: $type")
     }
-
-    open fun releaseCoroutines(): Boolean = false
 }