Drop synthetic class kind Function, drop Metadata#xi

compiler/backend/src/org/jetbrains/kotlin/codegen/ClosureCodegen.java

@@ -231,7 +231,6 @@ public class ClosureCodegen extends MemberCodegen<KtElement> {
             @Override
             public Unit invoke(AnnotationVisitor av) {
                 writeAnnotationData(av, serializer, functionProto, false);
-                av.visit(JvmAnnotationNames.SYNTHETIC_CLASS_KIND_FIELD_NAME, KotlinClassHeader.SyntheticClassKind.FUNCTION.getId());
                 return Unit.INSTANCE;
             }
         });

compiler/testData/codegen/boxWithStdlib/reflection/lambdaClasses/parameterNamesAndNullability.kt

@@ -34,17 +34,10 @@ fun extensionFunExpr() {
     assertEquals(null, g.parameters.single().name)
 }
 
-fun customFunction() {
-    val f = object : Function<String> {}
-    assertNull(f.reflect())
-}
-
 fun box(): String {
     lambda()
     funExpr()
     extensionFunExpr()
 
-    customFunction()
-
     return "OK"
 }