kernel-headers: remove deprecated and broken asm symlink fixups

[dtzWill]

Replaces #36303.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[dezgeg]

LGTM, though you could have a link to the discussion in #36303 on the commit message.

BTW, staging has quite a bit of unmerged stuff so might not want to merge this just yet.

[dtzWill]

Good call, updated the commit. Happy to wait re:merging to staging, but not sure how to know when it's in a better condition. Should I just ping this in a few days? :)

cc NixOS/rfcs#26 re:staging workflow .

(this is low-priority but will cause lots of rebuilds, while also being rather low risk in terms of "let's see if anything breaks")