Move remaining flake8 config to setup.cfg

Author: cdce8p

.flake8

@@ -25,6 +25,9 @@ include_trailing_comma = True
 skip_glob = tests/testdata
 
 [flake8]
+extend-ignore = E203,E266,E501,C901,F401
+max-complexity = 20
+select = B,C,E,F,W,T4,B9
 # Required for flake8-typing-imports (v1.12.0)
 # The plugin doesn't yet read the value from pyproject.toml
 min_python_version = 3.7.2