[llvm] [NFC][Offload] Clarify `olDestroyQueue` (PR #152132)

[Callum Fare via llvm-commits]

callumfare wrote:

> @callumfare Does it have to? I was thinking that it could be used in a context where you create a temporary queue, enqueue a bit of work to it, olDestroy it and then use the events generated from it to enqueue other work on. Essentially a simple way to implement out of order queues.

I suppose there's no reason it can't work that way, that's actually the behavior of `cuStreamDestroy`. I still think it's a bit of a foot-gun though, but I'm maybe too caught up in how UR and OpenCL do things.

https://github.com/llvm/llvm-project/pull/152132