Fix warning SYSLIB0051

> SYSLIB0051: 'Exception.Exception(SerializationInfo, StreamingContext)' is obsolete: 'This API supports obsolete formatter-based serialization. It should not be called or extended by application code.' (https://aka.ms/dotnet-warnings/SYSLIB0051)

Author: drewnoakes

src/NetMQ.Tests/ThrowingTraceListener.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Diagnostics;
-using System.Runtime.Serialization;
 
 namespace NetMQ.Tests
 {
@@ -19,7 +18,6 @@ public override void WriteLine(string? message)
         {
         }
 
-        [Serializable]
         public class DebugAssertFailureException : Exception
         {
             public DebugAssertFailureException()
@@ -33,10 +31,6 @@ public DebugAssertFailureException(string message) : base(message)
             public DebugAssertFailureException(string message, Exception inner) : base(message, inner)
             {
             }
-
-            protected DebugAssertFailureException(SerializationInfo info, StreamingContext context) : base(info, context)
-            {
-            }
         }
     }
 }