fixup: remove unused attribute

dotnet/src/Microsoft.Agents.AI.Workflows/StreamsMessageAttribute.cs

@@ -1,27 +0,0 @@
-// Copyright (c) Microsoft. All rights reserved.
-
-using System;
-using Microsoft.Shared.Diagnostics;
-
-namespace Microsoft.Agents.AI.Workflows;
-
-/// <summary>
-/// This attribute indicates that a message handler streams messages during its execution.
-/// </summary>
-[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
-public sealed class StreamsMessageAttribute : Attribute
-{
-    /// <summary>
-    /// The type of the message that the handler yields.
-    /// </summary>
-    public Type Type { get; }
-
-    /// <summary>
-    /// Indicates that the message handler yields streaming messages during the course of execution.
-    /// </summary>
-    public StreamsMessageAttribute(Type type)
-    {
-        // This attribute is used to mark executors that yield messages.
-        this.Type = Throw.IfNull(type);
-    }
-}