refactor(third_party): 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 //third_party

Change-Id: Ic382c0cdea7330a84d5f0b7d109c824ddceb94e7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2912
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

third_party/lisp/lisp-binary.nix

@@ -1,7 +1,7 @@
 # A library to easily read and write complex binary formats.
-{ depot, ... }:
+{ depot, pkgs, ... }:
 
-let src = depot.third_party.fetchFromGitHub {
+let src = pkgs.fetchFromGitHub {
   owner = "j3pic";
   repo = "lisp-binary";
   rev = "1aefc8618b7734f68697ddf59bc93cb8522aa0bf";