Nit fixes

Author: irvinesunday

src/Microsoft.OpenApi/Models/References/OpenApiExampleReference.cs

@@ -125,7 +125,7 @@ public override void SerializeAsV31(IOpenApiWriter writer)
         private void SerializeInternal(IOpenApiWriter writer,
             Action<IOpenApiWriter, IOpenApiReferenceable> action)
         {
-            Utils.CheckArgumentNull(writer);;
+            Utils.CheckArgumentNull(writer);
             action(writer, Target);
         }
     }

src/Microsoft.OpenApi/Reader/Services/OpenApiRemoteReferenceCollector.cs

@@ -1,7 +1,6 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
-using System;
 using System.Collections.Generic;
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Models;

test/Microsoft.OpenApi.Tests/Models/References/OpenApiExampleReferenceTests.cs

@@ -133,7 +133,7 @@ public OpenApiExampleReferenceTests()
 
         [Fact]
         public void ExampleReferenceResolutionWorks()
-        {
+         {
             // Assert
             Assert.NotNull(_localExampleReference.Value);
             Assert.Equal("[{\"id\":1,\"name\":\"John Doe\"}]", _localExampleReference.Value.Node.ToJsonString());