Cleanup descriptors.proto, regenerate

- move enums and messages nested in Callable to top level, since they're likely
  to be reused in other messages soon
- delete obsolete comments: some did not any value, some became obsolete with
  custom options ("id in StringTable" -> name_id_in_table)

compiler/builtins-serializer/src/org/jetbrains/kotlin/serialization/builtins/BuiltInsSerializerExtension.kt

@@ -55,7 +55,7 @@ public class BuiltInsSerializerExtension : SerializerExtension() {
         }
     }
 
-    override fun serializeValueParameter(descriptor: ValueParameterDescriptor, proto: ProtoBuf.Callable.ValueParameter.Builder) {
+    override fun serializeValueParameter(descriptor: ValueParameterDescriptor, proto: ProtoBuf.ValueParameter.Builder) {
         for (annotation in descriptor.annotations) {
             proto.addExtension(BuiltInsProtoBuf.parameterAnnotation, annotationSerializer.serializeAnnotation(annotation))
         }