…extra trait"

This reverts commit c37cb03. [This
commit] is squashed in the merge of PR #5, and does not exist in-tree.

microsoft/DirectXShaderCompiler#3793 has finally
been merged on October 13th 2022 and now allows us to drop the vtable
dummies for virtual destructors again, as those are not part of the ABI
and shouldn't have been in the vtable in the first place.

[This commit]: c37cb03

It's been quite a while ago (about two years) since we landed a whole
bunch of compatibility fixes for DXC, and I hope everyone is using
(much) newer releases by now.  I also doubt anyone is interested in
detailed descriptions of what we fixed (including the how and why), and
just wants a clear answer on the DXC release or commit they must
minimally use for compatibility with a certain `hassle-rs` release.