feat: remove unused setuptools import

Removed an unnecessary import of `setuptools` from `__main__.py`. This cleanup reduces the module's dependencies and potentially decreases startup time, making the codebase more efficient and lightweight. No significant functionality is affected by this change, consistent with our ongoing efforts to streamline the code.

src/deuthon/__main__.py

@@ -3,7 +3,6 @@
 import ast
 import tokenize
 import pathlib
-import setuptools
 import sys
 import traceback