[AWSX][Logs forwarder] Remove RDS source identification

[ge0Aja]

What does this PR do?

Pulling off RDS source, service and host identification from the logs forwarder as we start migrating code towards Datadog backend.

This should be released with version >= 4.0.0

This should not have any effects on the outcome of the log processing as we'll still be setting these in Datadog's backend.

Motivation

We've started working on a project to gradually remove complex logic from Lambda forwarder towards Datadog backend. We're starting with migrating the logic around defining source, service and host info for a log.
RDS is the first source we're migrating.

Testing Guidelines

Additional Notes

Types of changes

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

Check all that apply

• 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
• This PR passes the integration tests (ask a Datadog member to run the tests)
• This PR passes the unit tests
• This PR passes the installation tests (ask a Datadog member to run the tests)