Airflow 2.0 has been divided into two parts:
Apache Airflow Core, which includes webserver, scheduler, CLI and other components that are needed for minimal Airflow installation.
Providers packages - Providers packages include integrations with third party integrations. They are updated independently of the Apache Airflow core.
It was described in detail on the blog of one of the PMCs:
https://www.polidea.com/blog/airflow-2-providers/
In your case, you should look at the list of operators that are in provider packages:
https://airflow.apache.org/docs/apache-airflow-providers/operators-and-hooks-ref/index.html
Thus, you can find that the new class location is:
airflow.providers.amazon.aws.hooks.lambda_function.AwsLambdaHook
Documentation: https://airflow.apache.org/docs/apache-airflow-providers-amazon/stable/_api/airflow/providers/amazon/aws/hooks/lambda_function/index.html#module-airflow.providers.amazon.aws.hooks.lambda_function
You can also try to load the old class which should display a message.
>>> import airflow.contrib.hooks.aws_lambda_hook
/Users/X/airflow/airflow/contrib/hooks/aws_lambda_hook.py:29 DeprecationWarning: This module is deprecated. Please use `airflow.providers.amazon.aws.hooks.lambda_function`.