PR comments and minor cleanup

- "a parent binder" -> "the model binding system"
- remove unused `using`s

src/Microsoft.AspNet.Mvc.Abstractions/ModelBinding/ModelBindingContext.cs

@@ -187,8 +187,8 @@ public Type ModelType
         public bool IsTopLevelObject { get; set; }
 
         /// <summary>
-        /// Gets or sets an indication that a parent binder will make another binding attempt (e.g. fall back to the
-        /// empty prefix) after this one.
+        /// Gets or sets an indication that the model binding system will make another binding attempt (e.g. fall back
+        /// to the empty prefix) after this one.
         /// </summary>
         /// <remarks>
         /// Not passed into the model binding system but instead set by the top-level binder. With built-in binders,

src/Microsoft.AspNet.Mvc.Core/ModelBindingHelper.cs

@@ -2,10 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections;
 using System.Collections.Generic;
-using System.Diagnostics;
-using System.Globalization;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/BodyModelBinderTests.cs

@@ -10,7 +10,6 @@
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Http.Internal;
 using Microsoft.AspNet.Routing;
-using Microsoft.Framework.DependencyInjection;
 using Microsoft.Net.Http.Headers;
 using Moq;
 using Xunit;

test/Microsoft.AspNet.Mvc.Extensions.Test/Rendering/DefaultHtmlGeneratorTest.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.IO;
 using System.Linq;
 using Microsoft.AspNet.DataProtection;

test/Microsoft.AspNet.Mvc.IntegrationTests/ValidationIntegrationTests.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.IO;
-using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;