[llvm] [docs] Document which online sync-ups are no longer happening (PR #89361)

[Kristof Beyls via llvm-commits]

kbeyls wrote:

> These changes look fine to me. I can indeed confirm the Scalable Vectors & Arm SVE sync-ups are indeed no longer happening.
> 
> Just to be sure, did you build the HTML page to confirm that the table is rendered as expected?

Abolutely. The rendered result looks as follows:
<img width="1021" alt="Screenshot 2024-04-19 at 16 47 25" src="https://github.com/llvm/llvm-project/assets/19591946/4a185dd3-55e2-4435-b9b9-8b97fc69ca4d">


https://github.com/llvm/llvm-project/pull/89361