chore: Clean up (remove unused private variable)

Author: pawamoy

src/_griffe/loader.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import sys
 from contextlib import suppress
 from datetime import datetime, timezone
 from pathlib import Path
@@ -33,8 +32,6 @@
 
     from _griffe.enumerations import Parser
 
-_builtin_modules: set[str] = set(sys.builtin_module_names)
-
 
 class GriffeLoader:
     """The Griffe loader, allowing to load data from modules."""