Remove unnecessary static modifier

Author: artem-zinnatullin

src/main/java/rx/Notification.java

@@ -162,7 +162,7 @@ public void accept(Observer<? super T> observer) {
         }
     }
 
-    public static enum Kind {
+    public enum Kind {
         OnNext, OnError, OnCompleted
     }
 

src/main/java/rx/Single.java

@@ -147,7 +147,7 @@ public final static <T> Single<T> create(OnSubscribe<T> f) {
     /**
      * Invoked when Single.execute is called.
      */
-    public static interface OnSubscribe<T> extends Action1<SingleSubscriber<? super T>> {
+    public interface OnSubscribe<T> extends Action1<SingleSubscriber<? super T>> {
         // cover for generics insanity
     }
 
@@ -235,7 +235,7 @@ public <R> Single<R> compose(Transformer<? super T, ? extends R> transformer) {
      * 
      * @warn more complete description needed
      */
-    public static interface Transformer<T, R> extends Func1<Single<T>, Single<R>> {
+    public interface Transformer<T, R> extends Func1<Single<T>, Single<R>> {
         // cover for generics insanity
     }