refactor(ops): Consistent use of depot.third_party vs. pkgs

In preparation for the solution of b/108, we need to consistently use
`depot.third_party` for packages that are only packed in the TVL depot
and `pkgs` for things that come from nixpkgs.

This commit cleans up a huge chunk of these uses in //ops

Change-Id: I00faeb969eaa70760a26256274925b07998c2351
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2915
Tested-by: BuildkiteCI
Reviewed-by: sterni <[email protected]>

Original commit: https://code.tvl.fyi/patch/ops/kontemplate?id=9c5b5600ea3e8916af5715185ef57e57f36cf82b

Author: tazjin

default.nix

@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2019  Vincent Ambo <[email protected]>
+# Copyright (C) 2016-2021  Vincent Ambo <[email protected]>
 #
 # This file is part of Kontemplate.
 #
@@ -10,15 +10,15 @@
 # This file is the Nix derivation used to install Kontemplate on
 # Nix-based systems.
 
-{ depot, ... }:
+{ lib, pkgs, ... }:
 
-with depot.third_party; buildGoPackage rec {
+pkgs.buildGoPackage rec {
   name = "kontemplate-${version}";
   version = "canon";
   src = ./.;
   goPackagePath = "github.com/tazjin/kontemplate";
   goDeps = ./deps.nix;
-  buildInputs = [ parallel ];
+  buildInputs = [ pkgs.parallel ];
 
   # Enable checks and configure check-phase to include vet:
   doCheck = true;