Remove System.Linq.Async dependency.

eng/Packages.Data.props

@@ -72,7 +72,6 @@
     <PackageReference Update="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0" />
     <PackageReference Update="Microsoft.CSharp" Version="4.5.0" />
     <PackageReference Update="System.Collections.Immutable" Version="1.3.1" />
-    <PackageReference Update="System.Linq.Async" Version="4.0.0" />
 
     <!-- Azure SDK packages -->
     <PackageReference Update="Azure.Core" Version="1.10.0" />

sdk/resourcemanager/Azure.ResourceManager.Core/src/Azure.ResourceManager.Core.csproj

@@ -15,7 +15,6 @@
   <ItemGroup>
     <PackageReference Include="System.Collections.Immutable" />
     <PackageReference Include="Azure.ResourceManager.Resources" />
-    <PackageReference Include="System.Linq.Async" />
   </ItemGroup>
 
   <ItemGroup>

sdk/resourcemanager/Azure.ResourceManager.Core/src/Extensions/AsyncPageableExtensions.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Azure.ResourceManager.Core.Extensions
+{
+    internal static class AsyncPageableExtensions
+    {
+        public static async Task<TSource> FirstOrDefaultAsync<TSource>(
+            this AsyncPageable<TSource> source,
+            Func<TSource, bool> predicate,
+            CancellationToken token = default)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            token.ThrowIfCancellationRequested();
+
+            await foreach (var item in source.ConfigureAwait(false))
+            {
+                token.ThrowIfCancellationRequested();
+
+                if (predicate(item))
+                {
+                    return item;
+                }
+            }
+
+            return default;
+        }
+    }
+}

sdk/resourcemanager/Azure.ResourceManager.Core/src/ResourceOperationsBase.cs

@@ -7,6 +7,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Azure.Core;
+using Azure.ResourceManager.Core.Extensions;
 
 namespace Azure.ResourceManager.Core
 {