apple_sdk: remove cf-private alias

[ConnorBaker]

Description of changes

Removed use of the cf-private alias to darwin.apple_sdk.frameworks.CoreFoundation from Nixpkgs. Actual removal of the cf-private attribute will be done later, after the 23.05 release: #229389.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.05 Release Notes (or backporting 22.11 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.

[ConnorBaker]

This was unused in the derivation so I removed it as general cleanup.

[figsoda]

Should this maybe throw a warning first before turning into a hard error?

Also breaking changes are now restricted, see #223562

[wegank]

Let's only keep cf-private = self.apple_sdk.frameworks.CoreFoundation; then.

[ConnorBaker]

Created #229389 to track removal after 23.05 is cut.

@figsoda what's best practice for doing deprecations of the sort to alert out-of-tree users that the attribute is going away? Additionally, is there a schedule I should follow for that?