teleport_15: remove

[justinas]

Teleport 15 is expected to go EOL at around the time of NixOS 25.05 release (see https://goteleport.com/docs/upcoming-releases/).

This removes teleport_15, as well as all the version conditionals refering to versions 15 or 16 - the conditions were either version >= 15 (now always true), version >= 16 (now always true), or version < 16 (now always false).

Teleport 16 will be supported for most of the lifetime of NixOS 25.05, and Teleport 17, which has been made the default (see #393709), will be supported for the entirety of 25.05's lifetime..

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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[justinas]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 394056

---

x86_64-linux

✅ 4 packages built:

• teleport (teleport_17)
• teleport.client (teleport_17.client)
• teleport_16
• teleport_16.client

[JuliusFreudenberger]

Based on the commit activity I expect at least one more release for v15, but that can directly be applied for release-24.11 as well.
I think the decision dropping v15 and keeping v16 for 25.05 is right.