jack2: Don't use special libs for NetJack

[LordGrimmauld]

NetJack is little used and basically unmaintained. libopus [1] and celt [2] are only used for NetJack.

NetJack also supports an in-house implementation, which is sample-based. This means dropping celt and opus should not actually affect any users.

[1] https://github.com/search?q=repo%3Ajackaudio%2Fjack2+opus+NOT+path%3Acommon%2FJackNet*&type=code
[2] https://github.com/search?q=repo%3Ajackaudio%2Fjack2+celt+NOT+path%3Acommon%2FJackNet*&type=code

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[LordGrimmauld]

Pinged getchoo and jopejoe as they seem somewhat familiar with the audiostack around here, they maintain libopus. jack2 has no maintainers.