finagle-benchmark: Make sure the code compiles

Summary: Problem

This commit [1] broke a public API in Zk2Resolver's constructors.
For code with diamond dependencies this can cause problems.

Solution

This change use a constructor available in both implementations
to unblock developers.

[1] a9bb335

Differential Revision: https://phabricator.twitter.biz/D106064

finagle-benchmark/src/main/scala/com/twitter/finagle/serverset2/ServerSetResolver.scala

@@ -59,10 +59,7 @@ class ServerSetResolver {
 
     val stabilizationWindow = Duration.fromSeconds(stabilizationSec)
     val resolver = new Zk2Resolver(
-      NullStatsReceiver,
-      stabilizationWindow,
-      stabilizationWindow,
-      stabilizationWindow
+      NullStatsReceiver
     )
 
     val serverSetPaths = LocalServerSetService.createServerSetPaths(serverSetsToResolve)