The library is no longer needed when using the extension

[tianchu]

What does this PR do?

This library. will soon be deprecated for Lambda functions instrumented using the extension. Still required for existing customers using the forwarder.

Also remove some of the redundant information that already exists in the installation guide for java instrumentation https://docs.datadoghq.com/serverless/guide/datadog_forwarder_java/.

Motivation

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Checklist

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog