x2goclient: Use nx-libs instead of nxproxy

[srhb]

nxproxy was removed in favour of nx-libs, causing an eval failure in gcofborg (and possibly Hydra as well?) This should probably be reverted (or at least the nxproxy name should be removed instead of using lib.warn,) but this package also needs to refer to the nx-libs instead.

No real testing has been done here aside from running the executable -- I don't know the software.

See also #55723

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option 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/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

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[srhb]

Ah, it's only because the name only exists as an alias now, but this callPackage still depended on it. I think this should suffice to fix it. :)

[LnL7]

ofborg checks evaluation without aliases, either keep the warning in all-packages.nix or fix the remaining references.

[LnL7]

Oh ignore me, this was the fix. 😄

[Ma27]

@srhb thanks a lot for fixing that!