The range deleter waits between batches while holding the collection IX lock

In order to obey the rangeDeleterBatchDelayMS parameter, the range deleter sleeps between batches. However, it is doing so while under the collection lock. This means concurrent migrations (or rather anything that needs to take a strong lock) will block for up to that amount of time (default of 20ms). Instead, the wait should be happening after the lock is dropped.