refactor(wpcarro): Remove briefcase references

TL;DR:
- prefer WPCARRO env-var to BRIEFCASE
- remove repository URLs from Emacs libraries
- prefer tvl-depot-path where possible
- reduce the scope of constants.el
- prune (some not all) stale CI configuration

Change-Id: I21e9130402502ec6fa2fc4b46753c890069be62d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4545
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>

users/wpcarro/ci/pipelines/post-receive.nix

@@ -15,14 +15,6 @@ let
       command = "${pkgs.git-secrets}/bin/git-secrets --scan-history";
       label = ":broom: lint secrets";
     }
-    {
-      key = "build-briefcase";
-      command = ''
-        nix-build . -I briefcase="$(pwd)" --no-out-link --show-trace
-      '';
-      label = ":nix: build briefcase";
-      depends_on = "lint-secrets";
-    }
     {
       key = "init-emacs";
       command = let
@@ -32,25 +24,10 @@ let
         };
         runScriptEl = runScript {
           script = scriptEl;
-          briefcasePath = "$(pwd)";
         };
       in "${runScriptEl} ${initEl}";
       label = ":gnu: initialize Emacs";
-      depends_on = "build-briefcase";
-    }
-    {
-      key = "build-socrates";
-      command = ''
-        nix-build '<nixpkgs/nixos>' \
-          -I briefcase="$(pwd)" \
-          -I nixpkgs=/var/lib/buildkite-agent-socrates/nixpkgs-channels \
-          -I nixos-config=nixos/socrates/default.nix \
-          -A system \
-          --no-out-link \
-          --show-trace
-      '';
-      label = ":nix: build socrates";
-      depends_on = "build-briefcase";
+      depends_on = "lint-secrets";
     }
   ];
 in pkgs.writeText "pipeline.yaml" (toJSON pipeline)