Adjust flake8 config to be like other jupyterhub projects

Author: consideRatio

.flake8

@@ -3,10 +3,9 @@
 # E: style errors
 # W: style warnings
 # C: complexity
-# E402: module level import not at top of file
-# I100: Import statements are in the wrong order
-# I101: Imported names are in the wrong order. Should be
-ignore = E, C, W, E402, I100, I101, D400
+# D: docstring warnings (unused pydocstyle extension)
+# F841: local variable assigned but never used
+ignore = E, C, W, D, F841
 exclude =
     .cache,
     .github