update anymail config to use IAM role rather than access key

[hcientist]

from anymail docs for AWS SES

In addition, you must make sure boto3 is configured with AWS credentials having the necessary IAM permissions. There are several ways to do this; see Credentials in the Boto docs for options. Usually, an IAM role for EC2 instances, standard Boto environment variables, or a shared AWS credentials file will be appropriate. For more complex cases, use Anymail’s AMAZON_SES_CLIENT_PARAMS setting to customize the Boto session.

so probably just check boto config?