pyproject: Stop disabling urllib3 import checks in mypy

Double reasoning for this one:
* urllib3 now does have annotations
* since we don't import requests annotations (to avoid depending on typeshed)
  urllib3 annotations are never needed: we don't use urllib3 directly

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

Author: jku

pyproject.toml

@@ -152,6 +152,5 @@ disable_error_code = ["attr-defined"]
 module = [
   "requests.*",
   "securesystemslib.*",
-  "urllib3.*"
 ]
 ignore_missing_imports = "True"