Trimmed .flake8 exclusions

This .flake8 file was copied from wxflow.

.flake8

@@ -1,6 +1,3 @@
 [flake8]
-exclude = .git,.github,venv,__pycache__,docs/conf.py,old,build,dist
+exclude = .git,.github,venv,__pycache__,old,build,dist
 max-line-length = 160
-per-file-ignores =
-    # imported but unused
-    __init__.py: F401