Merge pull request ReactiveX#3342 from KevinTCoughlin/remove-unnecessary-onstart

Remove redundant onStart implementation in OperatorGroupBy

Author: abersnaze

src/main/java/rx/internal/operators/OperatorGroupBy.java

@@ -259,9 +259,6 @@ public void call() {
                         }
 
                     }).unsafeSubscribe(new Subscriber<T>(o) {
-                        @Override
-                        public void onStart() {
-                        }
                         @Override
                         public void onCompleted() {
                             o.onCompleted();