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 <sternenseemann@systemli.org>

ops/journaldriver/default.nix

@@ -1,11 +1,9 @@
-{ depot, ... }:
+{ depot, pkgs, ... }:
 
-with depot.third_party;
-
-naersk.buildPackage {
+depot.third_party.naersk.buildPackage {
   src = ./.;
 
-  buildInputs = [
+  buildInputs = with pkgs; [
     pkgconfig openssl systemd.dev
   ];
 }