lint: remove "evil" mypy setting

Author: dshemetov

pyproject.toml

@@ -88,9 +88,6 @@ disable = [
 
 [tool.mypy]
 ignore_missing_imports = true
-# TODO: The docs say that this setting is "evil". Maybe not?
-# https://mypy.readthedocs.io/en/latest/config_file.html#confval-strict_optional
-strict_optional = false
 disallow_incomplete_defs = true
 disallow_subclassing_any = true
 disallow_untyped_calls = true