Remove 19.09 support

Note there is still the 19.09 branch.

nix/sources.json

@@ -1,16 +1,4 @@
 {
-    "nixpkgs-19.09": {
-        "branch": "nixos-19.09",
-        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
-        "homepage": "https://github.com/NixOS/nixpkgs",
-        "owner": "NixOS",
-        "repo": "nixpkgs-channels",
-        "rev": "60c4ddb97fd5a730b93d759754c495e1fe8a3544",
-        "sha256": "1a1pvfz130c4cma5a21wjl7yrivc7ls1ksqqmac23srk64ipzakf",
-        "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/60c4ddb97fd5a730b93d759754c495e1fe8a3544.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
     "nixpkgs-20.03": {
         "branch": "nixos-20.03",
         "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",

tests/default.nix

@@ -1,9 +1,7 @@
 # Generate an attribute sets containing all tests for all releaeses
 # It looks like:
-# - extern.nixpkgs_19_09
 # - extern.nixpkgs_20.03
 # - extern.nixpkgs_unstable
-# - intern.nixpkgs_19_09
 # - intern.nixpkgs_20.03
 # - intern.nixpkgs_unstable
 
@@ -29,7 +27,6 @@ let
   };
 
   releaseNames = [
-    "nixpkgs-19.09"
     "nixpkgs-20.03"
     "nixpkgs-unstable"
   ];