getmail: drop

Stuck on python2 and there is a fork that isn't. Recommend getmail6
instead.

```
Traceback (most recent call last):
  File "/build/getmail-5.14/nix_run_setup", line 8, in <module>
    exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\\r\\n', '\\n'), __file__, 'exec'))
  File "setup.py", line 51
    print 'Default installation directories:'
          ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print('Default installation directories:')?
```

pkgs/tools/networking/getmail/default.nix

@@ -1,29 +0,0 @@
-{ lib, fetchurl, python2Packages }:
-
-python2Packages.buildPythonApplication rec {
-  pname = "getmail";
-  version = "5.14";
-
-  src = fetchurl {
-    url = "http://pyropus.ca/software/getmail/old-versions/${pname}-${version}.tar.gz";
-    sha256 = "1hcrd9h4g12f5gvl1djsbchcjry02ghq4icdr897s8v48pkrzagk";
-  };
-
-  doCheck = false;
-
-  postPatch = ''
-    # getmail spends a lot of effort to build an absolute path for
-    # documentation installation; too bad it is counterproductive now
-    sed -e '/datadir or prefix,/d' -i setup.py
-  '';
-
-  meta = {
-    description = "A program for retrieving mail";
-    maintainers = [ lib.maintainers.raskin ];
-    platforms = lib.platforms.linux;
-
-    homepage = "http://pyropus.ca/software/getmail/";
-    updateWalker = true;
-    license = lib.licenses.gpl2Plus;
-  };
-}

pkgs/top-level/aliases.nix

@@ -309,6 +309,7 @@ mapAliases ({
   gdb-multitarget = gdb; # added 2017-11-13
   gdk_pixbuf = gdk-pixbuf; # added 2019-05-22
   gettextWithExpat = gettext; # 2016-02-19
+  getmail = throw "getmail has been removed from nixpkgs, migrate to getmail6."; # added 2022-01-12
   giflib_4_1 = throw "giflib_4_1 has been removed; use giflib instead"; # 2020-02-12
   git-bz = throw "giz-bz has been removed from nixpkgs as it is stuck on python2."; # added 2022-01-01
   gitAndTools = self // { # added 2021-01-14

pkgs/top-level/all-packages.nix

@@ -5581,8 +5581,6 @@ with pkgs;
 
   geteltorito = callPackage ../tools/misc/geteltorito { };
 
-  getmail = callPackage ../tools/networking/getmail { };
-
   getmail6 = callPackage ../tools/networking/getmail6 { };
 
   getopt = callPackage ../tools/misc/getopt { };