serverless-pseudo-parameters deprecation warning

[marchuffnagle]

When deploying, a deprecation warning is being printed by serverless:

Serverless: Deprecation warning: "serverless-pseudo-parameters" plugin is no longer needed. Please uninstall it as it will not work with next Framework major release.
            Instead rely on "${aws:region}" and "${aws:accountId}" Serverless Framework variables

The documentation for that plugin indicates that it is deprecated as well: https://www.serverless.com/plugins/serverless-pseudo-parameters

From that plugin's readme:

With version v2.50.0, new variables sources ${aws:accountId} and ${aws:region} were introduced, which can be used in properties where CloudFormation pseudo paramaters cannot be used. Please use them instead of #{AWS::...} format as supported by this plugin

[philvarner]

Fix is to:

• remove all references to serverless-pseudo-parameters
• replace #{AWS::Region} with ${aws:region}, same for accountId