fix(wpcarro/nix): Remove <briefcase> references

Angle-bracketed references are a Nix anti-pattern, and thankfully this
repository enforces this as a standard.

TL;DR:
- Drop angle-bracketed references
- Change `briefcase` -> `users.wpcarro`
- Fix any resulting regressions
- Fix //users/wpcarro/tools/simple_vim
- Mark //users/wpcarro/boilerplate/typescript and related projects
  as broken
- drop .skip-subtree file, enabling depot CI

Change-Id: I7153cbabafa617bfd6b199370cbec65cb75441f6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4325
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/utils/default.nix

@@ -3,7 +3,7 @@ args@{ pkgs, ... }:
 # This top-level module exposes all of my utility functions for Nix. It should
 # be used like:
 # ```nix
-# inherit (briefcase.utils) fs;
+# inherit (depot.users.wpcarro.utils) fs;
 # ```
 
 let