[perf_witness] Remove debug print

Remove accidental debug print left behind in the UnixDomainSocket.bind.

Change-Id: I65b97eeca53226c508e689175028d02e6a6a6964
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/467561
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

Author: mraleph

pkg/perf_witness/lib/src/common.dart

@@ -73,14 +73,10 @@ abstract class UnixDomainSocket {
       io.File(path).deleteSync();
     }
 
-    final x = await io.ServerSocket.bind(
+    return await io.ServerSocket.bind(
       io.InternetAddress(path, type: io.InternetAddressType.unix),
       0,
     );
-
-    print('Server listening on $path: $x');
-
-    return x;
   }
 }