buku: fix build failing for bukuserver

SQLAlchemy-Utils v0.36.6 package override build is failing.

This is due to a patch in the original SQLAlchemy-Utils package which
broke the build of this package override:

```bash
> applying patch /nix/store/pd6anhwbf0in3r3jhi3sbn5v2fjs0mf2-skip-database-tests.patch
> patching file conftest.py
> Hunk #1 FAILED at 61.
> Hunk #2 succeeded at 98 (offset -10 lines).
```

These SQLAlchemy package overrides were originaly added to fix
incompatibilities with Flask-Admin.

See commit 05ae01f

However with Flask-Admin >= v1.5.6, several SQLAlchemy compatibility patches were added:
* https://flask-admin.readthedocs.io/en/latest/changelog/

We can now safely remove these package overrides to make bukuserver work again.

pkgs/applications/misc/buku/default.nix

@@ -1,26 +1,7 @@
 { lib, python3, fetchFromGitHub, withServer ? false }:
 
 let
-  python3' = python3.override {
-    packageOverrides = self: super: {
-      sqlalchemy = super.sqlalchemy.overridePythonAttrs (oldAttrs: rec {
-        version = "1.3.24";
-        src = oldAttrs.src.override {
-          inherit version;
-          hash = "sha256-67t3fL+TEjWbiXv4G6ANrg9ctp+6KhgmXcwYpvXvdRk=";
-        };
-        doCheck = false;
-      });
-      sqlalchemy-utils = super.sqlalchemy-utils.overridePythonAttrs (oldAttrs: rec {
-        version = "0.36.6";
-        src = oldAttrs.src.override {
-          inherit version;
-          sha256 = "0srs5w486wp5zydjs70igi5ypgxhm6h73grb85jz03fqpqaanzvs";
-        };
-      });
-    };
-  };
-  serverRequire = with python3'.pkgs; [
+  serverRequire = with python3.pkgs; [
     requests
     flask
     flask-admin
@@ -36,7 +17,7 @@ let
     toml
   ];
 in
-with python3'.pkgs; buildPythonApplication rec {
+with python3.pkgs; buildPythonApplication rec {
   version = "4.7";
   pname = "buku";