Bad link to the kernel-fusion extension doc

[GeorgeWeb]

Describe the bug

First, I want to start this with a pretext saying that I am sorry to the developers of fusion having to see their stellar work being removed and I am sure parts of it will aid future development.

The issue itself is a wrong link pointing to experimental now needs to be pointing to /removed which now breaks Doxygen builds.
As you can see in the latest CompilerAndRuntimeDesign.md#kernel-fusion-support there's still a link to kernel fusion in the experimental extensions directory instead of the removed extensions directory.

See the latest build job https://github.com/intel/llvm/actions/runs/10809701579/job/29989266991 from the Generate Doxygen documentation action.

To reproduce

No response

Environment

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Additional context

No response

[KornevNikita]

@sommerlukas hi, could you take a look please?

[GeorgeWeb]

I've posted a quick fix for the broken link here #15356 , but this section of the document would likely require better re-wording since it is now a removed extension.