secp256k1: move to top-level packages

Reason: secp256k1 is not a Python package.

pkgs/default.nix

@@ -13,6 +13,7 @@ let self = {
   extra-container = pkgs.callPackage ./extra-container { };
   clightning-plugins = import ./clightning-plugins pkgs self.nbPython3Packages;
   clboss = pkgs.callPackage ./clboss { };
+  secp256k1 = pkgs.callPackage ./secp256k1 { };
 
   nbPython3Packages = (pkgs.python3.override {
     packageOverrides = pySelf: super: import ./python-packages self pySelf;

pkgs/python-packages/default.nix

@@ -8,8 +8,7 @@ let
 in {
   bencoderpyx = callPackage ./bencoderpyx {};
   coincurve = callPackage ./coincurve {};
-  python-bitcointx = callPackage ./python-bitcointx {};
-  secp256k1 = callPackage ./secp256k1 {};
+  python-bitcointx = callPackage ./python-bitcointx { inherit (nbPkgs) secp256k1; };
   urldecode = callPackage ./urldecode {};
   chromalog = callPackage ./chromalog {};
   txzmq = callPackage ./txzmq {};