treewide: remove myself from a few more packages

* Stopped using wiki-js.
* I never really contributed to mpv, even though that apparently was the
plan a while ago.
* pydash was a reverse-dependency of privacyidea which I removed long
ago. Since then I haven't touched it anymore.

pkgs/applications/video/mpv/default.nix

···
     maintainers = with lib.maintainers; [
       fpletz
       globin
-      ma27
       SchweGELBin
     ];
     platforms = lib.platforms.unix;

pkgs/by-name/wi/wiki-js/package.nix

···
     homepage = "https://js.wiki/";
     description = "Modern and powerful wiki app built on Node.js";
     license = licenses.agpl3Only;
-    maintainers = with maintainers; [ ma27 ];
+    maintainers = with maintainers; [ ];
   };
 }

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

···
     homepage = "https://pydash.readthedocs.io";
     changelog = "https://github.com/dgilland/pydash/blob/v${version}/CHANGELOG.rst";
     license = licenses.mit;
-    maintainers = with maintainers; [ ma27 ];
+    maintainers = with maintainers; [ ];
   };
 }