Added ObsoleteAttribute to unused ViewEngine property

Fixes #5066

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewComponentResult.cs

@@ -52,10 +52,16 @@ namespace Microsoft.AspNetCore.Mvc
         public ITempDataDictionary TempData { get; set; }
 
         /// <summary>
+        /// <para>
+        /// This property is unused and will be removed in the next major version.
+        /// </para>
+        /// <para>
         /// Gets or sets the <see cref="IViewEngine"/> used to locate views.
+        /// </para>
         /// </summary>
         /// <remarks>When <c>null</c>, an instance of <see cref="ICompositeViewEngine"/> from
         /// <c>ActionContext.HttpContext.RequestServices</c> is used.</remarks>
+        [Obsolete("This property is unused and will be removed in the next major version.")]
         public IViewEngine ViewEngine { get; set; }
 
         /// <summary>