chore(docs): remove unnecessary line (#3933)

docs/developer-guide/unit-testing.md

@@ -191,9 +191,6 @@ class Test_iam_password_policy_uppercase:
         expiration=True,
     )
 
-    # We set a mocked aws_provider to unify providers, this way will isolate each test not to step on other tests configuration
-    aws_provider = set_mocked_aws_provider([AWS_REGION_US_EAST_1])
-
     # In this scenario we have to mock also the IAM service and the iam_client from the check to enforce    # that the iam_client used is the one created within this check because patch != import, and if you     # execute tests in parallel some objects can be already initialised hence the check won't be isolated.
     # In this case we don't use the Moto decorator, we use the mocked IAM client for both objects
     with mock.patch(