TimeWindowCompactionStrategy with unsafe_aggressive_sstable_expiration keeps overlaping SSTable references

When unsafe_aggressive_sstable_expiration is turned on, TWCS should not create or maintain an iterator of overlapping sstables. However, because TimeWindowCompactionController inherits from CompactionController and only sets ignoreOverlaps after the base class has constructed the overlap iterator, it ends up making an overlap iterator and then never updating it.

The end result is that such a compaction keeps references to lots of and likely all other SSTables on the node and thus delays the deletion of obsolete ones by hours or even days.