mido: Reduce dependances

According to [mido document][1], python-rtmidi is the default
recommended backend, the other backends are optional, and don't have all
features.

Remove pygame and rtmidi-python will reduce closure size from 930M to
87M, without losing functionality.

I've check nixpkgs, no other package use specific mido backends. Even if
they do need one, they can and should add the specific backend to their
own buildInputs/propagatedBuildInputs, as mido dynamically load these
python libraries, it will work as expected.

For reference, [ArchLinux][2] and [Debian][3] both make some backends
optional.

[1]: https://mido.readthedocs.io/en/latest/backends/index.html
[2]: https://aur.archlinux.org/packages/python-mido
[3]: https://packages.debian.org/buster/python3-mido

pkgs/development/python-modules/mido/default.nix

@@ -4,9 +4,7 @@
 , fetchPypi
 , substituteAll
 , portmidi
-, pygame
 , python-rtmidi
-, rtmidi-python
 , pytestCheckHook
 }:
 
@@ -27,9 +25,7 @@ buildPythonPackage rec {
   ];
 
   propagatedBuildInputs = [
-    pygame
     python-rtmidi
-    rtmidi-python
   ];
 
   checkInputs = [