Don't ignore XML doc warnings for Polly (#36485)

Author: BrennanConroy

src/HttpClientFactory/Polly/src/Microsoft.Extensions.Http.Polly.csproj

@@ -5,7 +5,6 @@
       The HttpClient factory is a pattern for configuring and retrieving named HttpClients in a composable way. This package integrates IHttpClientFactory with the Polly library, to add transient-fault-handling and resiliency through fluent policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback.
     </Description>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <NoWarn>$(NoWarn);CS1591</NoWarn>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <PackageTags>aspnetcore;httpclient</PackageTags>