Fix undefined behavior iterating over waiting keys

        // A copy is necessary here as we are changing the underlying map.  This would cause

        // undefined behavior if we iterated over the key set directly.

        ArraySet<String> keysToRemove = new ArraySet<>(mHeadsUpEntryMap.keySet());

        // Must get waiting keys before calling removeEntry, which clears waiting entries in

        // AvalancheController

        List<String> waitingKeysToRemove = mAvalancheController.getWaitingKeys();

        for (String key : keysToRemove) {

            removeEntry(key);

        }

        for (String key : mAvalancheController.getWaitingKeys()) {

        for (String key : waitingKeysToRemove) {

            removeEntry(key);

        }

    }