[core] Make it easier when profiling release builds

Don't write all log statements to the console in release
mode as it makes it a bit harder to perf profile things.

Author: alanmcgovern

src/SampleClient/main.cs

@@ -55,8 +55,9 @@ static void Main (string[] args)
 
         private static async Task StartEngine ()
         {
+#if DEBUG
             Logger.Factory = (string className) => new TextLogger (Console.Out, className);
-
+#endif
             int port;
             Torrent torrent = null;
             // Ask the user what port they want to use for incoming connections