Local index got corrupted if intermediate compaction happen during the split.

The scenario is quite simple:
If we trigger split after index creation when we have a lot of HFiles not yet compacted, the compaction may happen for part of those files and the scan type will be COMPACT_RETAIN_DELETES, but not COMPACT_DROP_DELETES as we expect in preCompactScannerOpen. In this case the regular scanner will be used during compaction and we get incorrectly data in the local index. Discussed it with enis offline and it seems that the check for COMPACT_DROP_DELETES is not necessary and can/should be deleted.