texlive: drop unused "fetch&unpack" derivations (#126982)
texlive: drop unused "fetch&unpack" derivations (#126982)

Motivations
- not well reproducible as they disable hashed mirrors (tarballs.nixos.org)
- only reachable by modifying the file pkgs.nix, thus unused
- the space saving is analogous to using substitutes
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs