Use default value for `RabbitMQActivitySource.UseRoutingKeyAsOperatio…

…nName`

The default is `true`, anyway. No need to set it here.

Pointed out by @kielex in this comment:
#1533 (comment)

projects/RabbitMQ.Client.OpenTelemetry/TraceProviderBuilderExtensions.cs

@@ -12,7 +12,6 @@ public static class OpenTelemetryExtensions
     {
         public static TracerProviderBuilder AddRabbitMQInstrumentation(this TracerProviderBuilder builder)
         {
-            RabbitMQActivitySource.UseRoutingKeyAsOperationName = true;
             RabbitMQActivitySource.ContextExtractor = OpenTelemetryContextExtractor;
             RabbitMQActivitySource.ContextInjector = OpenTelemetryContextInjector;
             builder.AddSource("RabbitMQ.Client.*");