Only require the core libraries of aws-sdk

[ivomurrell]

Only include the library files from aws-sdk rather than the whole module. This means module bundler tools like webpack can tree shake the API JSON files of unused services when including http-aws-es as a dependency. Doing so can massively reduce bundle size of dependents.

Following advice from AWS's documentation on webpack: https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/webpack.html