Clustering : Remove actorFor (deprecated) call from TransactionProxy.java

Its used on line#401 in method public Future<ActorPath> readyTransaction().

actorFor is deprecated. ActorSelection can be used instead.

Also, on line#395,
String resolvedCohortPath = getResolvedCohortPath(reply.getCohortPath().toString());

there is no need to convert the ActorPath got from reply.getCohortPath(). This can directly be used if line#401 is changed to use actor selection.