pythonPackages.supervisor: drop meld3 dependency

supervisor no longer depends on meld3 as of version 4.1.0

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

@@ -1,6 +1,5 @@
 { stdenv, lib, buildPythonPackage, isPy3k, fetchPypi
 , mock
-, meld3
 , pytest
 , setuptools
 }:
@@ -22,7 +21,7 @@ buildPythonPackage rec {
     pytest
   '';
 
-  propagatedBuildInputs = [ meld3 setuptools ];
+  propagatedBuildInputs = [ setuptools ];
 
   meta = with lib; {
     description = "A system for controlling process state under UNIX";