Remove outdated sample for field-only properties

Fixes #1257

entity-framework/core/modeling/backing-field.md

@@ -49,12 +49,8 @@ You can give EF the name of the field in the `Property(...)` API. If there is no
 
 [!code-csharp[Main](../../../samples/core/Modeling/FluentAPI/BackingFieldNoProperty.cs#Sample)]
 
-You can also choose to give the property a name, other than the field name. This name is then used when creating the model, most notably it will be used for the column name that is mapped to in the database.
-
-[!code-csharp[Main](../../../samples/core/Modeling/FluentAPI/BackingFieldConceptualProperty.cs#Sample)]
-
 When there is no property in the entity class, you can use the `EF.Property(...)` method in a LINQ query to refer to the property that is conceptually part of the model.
 
 ``` csharp
-var blogs = db.blogs.OrderBy(b => EF.Property<string>(b, "Url"));
+var blogs = db.blogs.OrderBy(b => EF.Property<string>(b, "_validatedUrl"));
 ```