Mark value constructor getters as @ignore

This is not a whole true, however, because the model loader does
still look at them, at least in order to support importing constructors
as in #2176. But we don't want the model loader to see them as methods.

Part of ceylon/ceylon.language#757

src/com/redhat/ceylon/compiler/java/codegen/CeylonVisitor.java

@@ -275,7 +275,7 @@ protected void transformSingletonConstructor(
                 null, 
                 singletonModel.getName(), singletonModel, false);
         adb.modelAnnotations(gen.makeAtEnumerated());
-
+        adb.modelAnnotations(gen.makeAtIgnore());
         adb.userAnnotations(gen.expressionGen().transformAnnotations(false, OutputElement.GETTER, ctor));
         adb.fieldAnnotations(gen.expressionGen().transformAnnotations(false, OutputElement.FIELD, ctor));
         adb.immutable();// not setter