Fixed other warnings to allow Netcore build to work.

Author: MiYanni

src/Common/Commands.Common.Authentication/Authentication/UserTokenProvider.Netcore.cs

@@ -29,8 +29,6 @@ namespace Microsoft.Azure.Commands.Common.Authentication
     /// </summary>
     internal class UserTokenProvider : ITokenProvider
     {
-        Action<string> _promptAction = null;
-
         public UserTokenProvider()
         {
         }

src/ResourceManager/Reservations/Commands.Reservations/Common/AzureReservationsCmdletBase.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
@@ -19,8 +18,6 @@ public abstract class AzureReservationsCmdletBase : AzureRMCmdlet
     {
         private IAzureReservationAPIClient _azureReservationAPI;
 
-        private Dictionary<string, List<string>> _defaultRequestHeaders;
-
         /// <summary>
         /// Gets or sets the Reservations management client.
         /// </summary>