Configure mypy and flake8 for our re-export files

This removes the need to use __all__ in these files, while also
allowing us to have strictness elsewhere in the codebase.

jedi/inference/value/__init__.py

@@ -1,21 +1,9 @@
+# Re-export symbols for wider use. We configure mypy and flake8 to be aware that
+# this file does this.
+
 from jedi.inference.value.module import ModuleValue
 from jedi.inference.value.klass import ClassValue
 from jedi.inference.value.function import FunctionValue, \
     MethodValue
 from jedi.inference.value.instance import AnonymousInstance, BoundMethod, \
     CompiledInstance, AbstractInstanceValue, TreeInstance
-
-__all__ = (
-    'ModuleValue',
-
-    'ClassValue',
-
-    'FunctionValue',
-    'MethodValue',
-
-    'AnonymousInstance',
-    'BoundMethod',
-    'CompiledInstance',
-    'AbstractInstanceValue',
-    'TreeInstance',
-)