flake8 is not needed to run tests.

--- pyproject_hooks-1.2.0/dev-requirements.txt.orig
+++ pyproject_hooks-1.2.0/dev-requirements.txt
@@ -1,5 +1,4 @@
 pytest
-flake8
 testpath
 setuptools>=30
 tomli >=1.1.0 ; python_version<'3.11'