HashSet iteration on drop not elided for Copy elements

[bluss]

If a HashSet has Copy elements, it doesn't need to visit all elements on drop. The iteration in RawTable's drop still is computed even if the elements have no destructors, which leads to O(n) average complexity even then.

[hanna-kruppe]

To be clear, this is also in release mode, right? A while back there was a similar issue for vec but AFAIK that one was only about debug mode.

[bluss]

Yes, also in release mode.