RTS to clear the HS flag of an update following tombstone

Rollback to stable clears the WT_UPDATE_HS flag whenever a stable update is found in the update list. In case if the found update is a tombstone, the tombstone is always written with a following update to the data store. Having an update that is written to the data store with a flag of HS is wrong.

As part of RTS, clear the WT_UPDATE_HS flag of an update following tombstone if exists in the update list.