Explicitly mark destructors with override (#13212)

Explicitly mark destructors with override (#13212)

Summary:
I saw these compiler warnings while preparing for the 9.10 release:

```cpp
'~CompactOnDeletionCollectorFactory' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]

'~CompactForTieringCollectorFactory' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]
```

This code is from a while ago so I assume that this CI check has been failing for quite some time. We should still clean this up to avoid confusion in the future.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/13212

Test Plan: Existing CI checks should pass, and we should not see this CI check failure the next time we try to make a release/patch.

Reviewed By: jaykorean

Differential Revision: D67287794

Pulled By: archang19

fbshipit-source-id: a11230a919c0b7ef21a7219bf05f567d3d44b2d1