tree-wide: remove flexagoon from maintainers

> You can remove me from all of my packages if there are any left, I'm no longer using Nix and no longer maintain any packages

https://github.com/NixOS/nixpkgs/pull/290682#issuecomment-1974827679

maintainers/maintainer-list.nix

···
     githubId = 1952914;
     name = "Maxence Maireaux";
   };
-  flexagoon = {
-    email = "[e-mail]";
-    github = "flexagoon";
-    githubId = 66178592;
-    name = "Pavel Zolotarevskiy";
-  };
   flexiondotorg = {
     name = "Martin Wimpress";
     email = "[e-mail]";

pkgs/data/themes/gtk-theme-framework/default.nix

···
   meta = with lib; {
     homepage = "https://github.com/jaxwilko/gtk-theme-framework";
     license = licenses.gpl3Only;
-    maintainers = with maintainers; [ flexagoon ];
+    maintainers = with maintainers; [ ];
   };
 }

pkgs/data/themes/kwin-decorations/kde-rounded-corners/default.nix

···
     description = "Rounds the corners of your windows";
     homepage = "https://github.com/matinlotfali/KDE-Rounded-Corners";
     license = licenses.gpl3Only;
-    maintainers = with maintainers; [ flexagoon ];
+    maintainers = with maintainers; [ ];
   };
 }

pkgs/data/themes/kwin-decorations/sierra-breeze-enhanced/default.nix

···
     homepage = "https://github.com/kupiqu/SierraBreezeEnhanced";
     changelog = "https://github.com/kupiqu/SierraBreezeEnhanced/releases/tag/V${version}";
     license = licenses.gpl3Only;
-    maintainers = with maintainers; [ flexagoon ];
+    maintainers = with maintainers; [ ];
   };
 }