ceph: fixup the embedded sqlalchemy

This version-override approach is annoying me, as the original
derivation is then supposed to support multiple versions
without knowing about it. And naturally it tends to break.
(this time on 446a8703c3b)
https://hydra.nixos.org/build/228178995/nixlog/3/tail

pkgs/tools/filesystems/ceph/default.nix

···
           inherit version;
           hash = "sha256-aRO4JH2KKS74MVFipRkx4rQM6RaB8bbxj2lwRSAMSjA=";
         };
-        nativeCheckInputs = oldAttrs.nativeCheckInputs ++ (with super; [
-          pytest-xdist
-        ]);
-        disabledTestPaths = (oldAttrs.disabledTestPaths or []) ++ [
+        disabledTestPaths = [
           "test/aaa_profiling"
           "test/ext/mypy"
         ];