Compaction leftovers not removed on upgrade 2.1/2.2 -> 3.0

Before 3.0 we used sstable ancestors to figure out if an sstable was left over after a compaction. In 3.0 the ancestors are ignored and instead we use LogTransaction files to figure it out. 3.0 should still clean up 2.1/2.2 compaction leftovers using the on-disk sstable ancestors when available.