feat(nix): simplify flake.nix, remove devenv

.envrc

@@ -4,8 +4,6 @@ if ! has nix_direnv_version || ! nix_direnv_version 3.1.0; then
   source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.1.0/direnvrc" "sha256-yMJ2OVMzrFaDPn7q8nCBZFRYpL/f0RcHzhmw/i6btJM="
 fi
 
-export DEVENV_IN_DIRENV_SHELL=true
-
 # Load .env file if present
 dotenv_if_exists
 
@@ -20,5 +18,5 @@ if [[ -f .envrc.local ]]; then
 fi
 
 if ! use flake . --no-pure-eval; then
-  echo "Devenv could not be built. The devenv environment was not loaded. Make the necessary changes to flake.nix and hit enter to try again." >&2
+  echo "Development shell could not be built. The environment was not loaded. Make the necessary changes to flake.nix and hit enter to try again." >&2
 fi