python3Minimal and python3: don't override python3
python3Minimal and python3: don't override python3

This reduces the amount of packages that are required to use
builtins.fetchurl to fetch. Without this change, mime-types
would not be able to use fetchzip when mime-types support is
added to python3.

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