Today we make sure that a 5.x index commit should have all required
commit tags in RecoveryTarget#cleanFiles method. The reason we do this
in RecoveryTarget#cleanFiles method because this is only needed in a
file-based recovery and we assume that #cleanFiles should be called in a
file-based recovery. However, this assumption is not valid if the index
is sealed (.i.e synced-flush). This incorrect assumption would prevent
users from rolling upgrade from 5.x to 6.3 if their index were sealed.