Remove unused useSyntaxTreeCache option

[majocha]

Clean up.
This functionality is no longer configurable, and that cache no longer exists as a separate value in the builder.
Instead SyntaxTree caching occurs naturally by preserving GraphNode computed values, IIRC.

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.200.md
vsintegration/src	docs/release-notes/.VisualStudio/17.12.md

[psfinaki]

I think surface area will need an update as well.

[majocha]

The consensus is to remove it. It was also still marked experimental.

[psfinaki]

I just noticed it's also present in VS settings. I think we should remove it there as well then :)

[psfinaki]

(use_syntax_tree_cache)

[majocha]

I think this is already done in this PR.

[psfinaki]

Right, sorry, I somehow mis-scrolled it 🤦 Thanks!

[psfinaki]

Thanks, I think this PR can serve as a good manual on how to add / remove an option to the compiler and propagate / unpropagate it everywhere :)

[psfinaki]

Oh I know what I meant. This is still left in the resources via keywords, here. So can be removed there as well.

[majocha]

Right, couldn't find anything with search in files, makes sense now :)