remove no_implicit_optional

this is the default in mypy 0.990

Committed via https://github.com/asottile/all-repos

Author: asottile

setup.cfg

@@ -75,7 +75,6 @@ check_untyped_defs = true
 disallow_any_generics = true
 disallow_incomplete_defs = true
 disallow_untyped_defs = true
-no_implicit_optional = true
 warn_redundant_casts = true
 warn_unused_ignores = true