Optimize the Range Deleter speed

The sharding range deleter was intentionally implemented to not be fully efficient in order to minimize its interference with MMAP V1. This causes orphaned data to accumulate especially with the recent moveChunk improvements.

With the WiredTiger storage engine, we can let it run at full speed and we should investigate the benefit of directly instantiating an auto-yielding delete stage instead of recreating the index scan phase for each document.