treewide: remove nand0p as maintainer

While looking at the sphinx package I noticed it was heavily
undermaintained, which is when we noticed nand0p has been inactive for
roughly 18 months. It is therefore prudent to assume they will not be
maintaining their packages, modules and tests.

- Their last contribution to nixpkgs was in 2019/12
- On 2021/05/08 I wrote them an email to the address listed in the
  maintainer-list, which they didn't reply to.

pkgs/development/python-modules/isort/4.nix

@@ -38,6 +38,6 @@ in buildPythonPackage rec {
     description = "A Python utility / library to sort Python imports";
     homepage = "https://github.com/timothycrosley/isort";
     license = licenses.mit;
-    maintainers = with maintainers; [ couchemar nand0p ];
+    maintainers = with maintainers; [ couchemar ];
   };
 }

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

@@ -72,6 +72,6 @@ in buildPythonPackage rec {
     description = "A Python utility / library to sort Python imports";
     homepage = "https://github.com/PyCQA/isort";
     license = licenses.mit;
-    maintainers = with maintainers; [ couchemar nand0p ];
+    maintainers = with maintainers; [ couchemar ];
   };
 }