gns3-{server-gui}: Fix build

Removed duplicate overrides and made the override interface consistent.
The previous method of pinning caused frequent breakages.

pkgs/applications/networking/gns3/default.nix

@@ -20,7 +20,9 @@ let
         });
       };
     commonOverrides = [
-      (mkOverride "jsonschema" "3.2.0" "0ykr61yiiizgvm3bzipa3l73rvj49wmrybbfwhvpgk3pscl5pa68")
+      (self: super: {
+        jsonschema = super.jsonschema_3;
+      })
     ];
   };
   mkGui = args: libsForQt5.callPackage (import ./gui.nix (addVersion args // extraArgs)) { };

pkgs/applications/networking/gns3/gui.nix

@@ -10,6 +10,7 @@
 , python3
 , fetchFromGitHub
 , wrapQtAppsHook
+, packageOverrides ? self: super: {}
 }:
 
 let
@@ -17,21 +18,7 @@ let
   ];
 
   python = python3.override {
-    packageOverrides = lib.foldr lib.composeExtensions (self: super: {
-      jsonschema = super.jsonschema.overridePythonAttrs (oldAttrs: rec {
-        version = "3.2.0";
-
-        src = super.fetchPypi {
-          inherit (oldAttrs) pname;
-          inherit version;
-          sha256 = "sha256-yKhbKNN3zHc35G4tnytPRO48Dh3qxr9G3e/HGH0weXo=";
-        };
-
-        SETUPTOOLS_SCM_PRETEND_VERSION = version;
-
-        doCheck = false;
-      });
-    }) defaultOverrides;
+    packageOverrides = lib.foldr lib.composeExtensions (self: super: { }) ([ packageOverrides ] ++ defaultOverrides);
   };
 in python.pkgs.buildPythonPackage rec {
   pname = "gns3-gui";

pkgs/applications/networking/gns3/server.nix

@@ -14,22 +14,6 @@
 
 let
   defaultOverrides = commonOverrides ++ [
-    (self: super: {
-      jsonschema = super.jsonschema.overridePythonAttrs (oldAttrs: rec {
-        version = "3.2.0";
-
-        src = super.fetchPypi {
-          inherit (oldAttrs) pname;
-          inherit version;
-          sha256 = "sha256-yKhbKNN3zHc35G4tnytPRO48Dh3qxr9G3e/HGH0weXo=";
-        };
-
-        SETUPTOOLS_SCM_PRETEND_VERSION = version;
-
-        doCheck = false;
-      });
-
-    })
   ];
 
   python = python3.override {