Merge branch 'toms-open-coding-config-import' into 'develop'

Grid configs: clean up config imports

See merge request !269

morph/grid/local/grid.nix

 let
-  pkgs = import <nixpkgs> { };
-
   gridlib = import ../../lib;
-  grid-config = pkgs.lib.trivial.importJSON ./config.json;
+  grid-config = builtins.fromJSON (builtins.readFile ./config.json);
 
   ssh-users = let
     ssh-users-file = ./public-keys/users.nix;

morph/grid/production/grid.nix

 # See morph/grid/local/grid.nix for additional commentary.
 let
-  pkgs = import <nixpkgs> { };
-
   gridlib = import ../../lib;
-  grid-config = pkgs.lib.trivial.importJSON ./config.json;
+  grid-config = builtins.fromJSON (builtins.readFile ./config.json);
 
   # Module with per-grid configuration
   grid-module = {config, ...}: {

morph/grid/testing/grid.nix

 # See morph/grid/local/grid.nix for additional commentary.
 let
-  pkgs = import <nixpkgs> { };
-
   gridlib = import ../../lib;
-  grid-config = pkgs.lib.trivial.importJSON ./config.json;
+  grid-config = builtins.fromJSON (builtins.readFile ./config.json);
 
   # Module with per-grid configuration
   grid-module = {config, ...}: {