93d77a27d2
Summary: The pre-existing code was purging a DeleteMarker if thay key did not exist in deeper levels. But in the Universal Compaction Style, all files are in Level0. For compaction runs that did not include the earliest file, we were erroneously purging the DeleteMarkers. The fix is to purge DeleteMarkers only if the compaction includes the earlist file. Test Plan: DBTest.Randomized triggers this code path. Differential Revision: https://reviews.facebook.net/D12081