Remove unneccessary crypto using

Author: marcpopMSFT

src/Containers/Microsoft.NET.Build.Containers/Tasks/ComputeDotnetBaseImageAndTag.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics.CodeAnalysis;
-using System.Security.Cryptography;
 using Microsoft.Build.Framework;
 using NuGet.Versioning;
 #if NETFRAMEWORK