Get rid of nixpkgs everywhere and use pkgs arguments instead

pkgs/lightning-charge.nix

@@ -1,6 +1,4 @@
-{pkgs ? import <nixpkgs> {
-    inherit system;
-  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
+{pkgs, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
 
 
 with pkgs;

pkgs/nanopos.nix

@@ -1,6 +1,4 @@
-{pkgs ? import <nixpkgs> {
-    inherit system;
-  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
+{pkgs, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
 
 
 with pkgs;

pkgs/nodeinfo.nix

@@ -1,5 +1,6 @@
-with import <nixpkgs> {}; # bring all of Nixpkgs into scope
+{pkgs}:
 
+with pkgs;
 stdenv.mkDerivation {
   name = "nodeinfo";
   src = ./nodeinfo.sh;

pkgs/spark-wallet.nix

@@ -1,6 +1,4 @@
-{pkgs ? import <nixpkgs> {
-    inherit system;
-  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
+{pkgs, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-8_x"}:
 
 
 with pkgs;