This PR mainly addresses `python3.6` deprecation, but it also updates deprecation verbiage for other runtimes as well.

```
Hello,

We are contacting you as we have identified that your AWS Account currently has one or more Lambda functions using Python 3.6 runtime.

We are ending support for Python 3.6 in AWS Lambda. This follows Python 3.6 End-Of-Life (EOL) reached on December 23, 2021 [1].

As described in the Lambda runtime support policy [2], end of support for language runtimes in Lambda happens in two stages. Starting July 18, 2022, Lambda will no longer apply security patches and other updates to the Python 3.6 runtime used by Lambda functions, and functions using Python 3.6 will no longer be eligible for technical support. In addition, you will no longer be able to create new Lambda functions using the Python 3.6 runtime. Starting August 17, 2022, you will no longer be able to update existing functions using the Python 3.6 runtime.

We recommend that you upgrade your existing Python 3.6 functions to Python 3.9 before August 17, 2022.

End of support does not impact function execution. Your functions will continue to run. However, they will be running on an unsupported runtime which is no longer maintained or patched by the AWS Lambda team.

The following command shows how to use the AWS CLI [3] to list all functions in a specific region using Python 3.6. To find all such functions in your account, repeat this command for each region:

aws lambda list-functions --function-version ALL --region us-east-1 --output text --query "Functions[?Runtime=='python3.6'].FunctionArn"

If you have any concerns or require further assistance, please contact AWS Support [4].
```

https://docs.aws.amazon.com/lambda/latest/dg/runtime-support-policy.html

Link aws#19988 

----

### All Submissions:

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### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Since aws/aws-cdk#19938 AWS CDK has added native deprecation annotations to runtimes,
allowing us to remove some code!

Since it was originally introduced in #1007,
AWS CDK has added native deprecation annotations to runtimes in aws/aws-cdk#19938 AWS CDK.

The means we can remove some code!

Since it was originally introduced in #1007,
AWS CDK has added native deprecation annotations to runtimes in aws/aws-cdk#19938.

The means we can remove some code!