Removed UseTransportThread (#1781)

src/Microsoft.AspNetCore.Server.Kestrel.Core/KestrelServerOptions.cs

@@ -29,11 +29,6 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core
         /// </remarks>
         public bool AddServerHeader { get; set; } = true;
 
-        /// <summary>
-        /// Gets or sets a value that determines if Kestrel should use the transport thread thread when executing user code.
-        /// </summary>
-        public bool UseTransportThread { get; set; }
-
         /// <summary>
         /// Gets or sets a value that determines how Kestrel should schedule user callbacks.
         /// </summary>