Change subscription remove logic.

Author: egetman

tck/src/test/java/org/reactivestreams/tck/PublisherVerificationTest.java

@@ -787,13 +787,7 @@ public void request(long n) {
             public void cancel() {
               canceled.set(true);
               subscriber = null;
-              // COR list, so its ok to remove demand that way
-              for (CancelableSubscription subscription : subscriptions) {
-                // reference equality. It's ok
-                if (subscription == this) {
-                  subscriptions.remove(subscription);
-                }
-              }
+              subscriptions.remove(this);
             }
           }