Port C# client perf fix to release (#2189)

src/Microsoft.AspNetCore.SignalR.Client.Core/HubConnection.cs

@@ -530,9 +530,6 @@ namespace Microsoft.AspNetCore.SignalR.Client
 
         private async Task DispatchInvocationAsync(InvocationMessage invocation)
         {
-            // Make sure we get off the main event loop before we dispatch into user code
-            await AwaitableThreadPool.Yield();
-
             // Find the handler
             if (!_handlers.TryGetValue(invocation.Target, out var invocationHandlerList))
             {