chore(nix->guix): delete Nix estate-wide (#138) (#47)

Automated sweep to eradicate Nix from the estate as Guix is now the sole
reproducible environment.

Author: hyperpolymath

.envrc

@@ -14,7 +14,6 @@ fi
 
 # Load Nix flake if flake.nix exists
 if has nix && [ -f flake.nix ]; then
-  use flake
 fi
 
 # Project environment variables

.github/workflows/hypatia-scan.yml

@@ -412,4 +412,4 @@ jobs:
               repo: context.repo.repo,
               issue_number: context.issue.number,
               body: comment
-            });
+            });