remove an index level block if its empty (make no sense to keep an empty set for it, also, shouldn't shot it back in APIs)

modules/elasticsearch/src/main/java/org/elasticsearch/cluster/block/ClusterBlocks.java

@@ -199,6 +199,9 @@ public class ClusterBlocks {
                 return this;
             }
             indices.get(index).remove(block);
+            if (indices.get(index).isEmpty()) {
+                indices.remove(index);
+            }
             return this;
         }