Clean up overlays and remove obsolete dependencies

overlays/patches/default.nix

@@ -2,10 +2,13 @@ _final: prev:
 (import ./abseil { inherit prev; })
 // {
   gnutls = import ./gnutls { inherit (prev) gnutls; };
+  prometheus = import ./prometheus { inherit (prev) prometheus; };
 
   pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
     (_pythonFinal: pythonPrev: {
-      scipy = import ./scipy { inherit (pythonPrev) scipy; };
+      backrefs = import ./backrefs { inherit (pythonPrev) backrefs; };
+      pytest-xdist = import ./pytest-xdist { inherit (pythonPrev) pytest-xdist; };
+      sentry-sdk = import ./sentry-sdk { inherit (pythonPrev) sentry-sdk; };
       torchcodec = import ./torchcodec { inherit (pythonPrev) torchcodec; };
     })
   ];