Remove a redundant annotation. (#1005)

Author: songy23

contrib/zpages/src/main/java/io/opencensus/contrib/zpages/StatszZPageHandler.java

@@ -539,7 +539,7 @@ private StatszZPageHandler(ViewManager viewManager) {
    */
   private static class TreeNode {
     // Only leaf nodes have views.
-    @javax.annotation.Nullable final /*@Nullable*/ View view;
+    @javax.annotation.Nullable final View view;
 
     // A mapping from relative path to children TreeNodes. Sorted by the relative path.
     SortedMap<String, TreeNode> children = Maps.newTreeMap();