pythonPackages.lmtpd: upgrade to Python 3
pythonPackages.lmtpd: upgrade to Python 3

Python 2 support was dropped on
https://github.com/moggers87/lmtpd/commit/3546d4660f8229b3d6375aebf9e56ea88a93cbb0

ZHF: #97479
https://hydra.nixos.org/build/127641301

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