Remove unnecessary async state machine from DefaultHttpRetryHandler (#…

…678)

### Motivation and Context

Small bit of unnecessary overhead.

### Description

Removes one or more allocations every time it needs to delay.

dotnet/src/SemanticKernel.Abstractions/Reliability/DefaultHttpRetryHandler.cs

@@ -138,9 +138,9 @@ internal interface IDelayProvider
 
     internal class TaskDelayProvider : IDelayProvider
     {
-        public async Task DelayAsync(TimeSpan delay, CancellationToken cancellationToken)
+        public Task DelayAsync(TimeSpan delay, CancellationToken cancellationToken)
         {
-            await Task.Delay(delay, cancellationToken).ConfigureAwait(false);
+            return Task.Delay(delay, cancellationToken);
         }
     }