internal/trace/listener: Don't override service name

[piochelepiotr]

What does this PR do?

Today, if DD_SERVICE is used, the service name is still set to aws.lambda.
This PR removes that logic, and uses the defaults of the Go tracer (so defaulting to the binary name).

Motivation

Testing Guidelines

Behavior before:

Traces have a service name aws.lambda is DD_SERVICE isn't set
Data streams have a service aws.lambda if DD_SERVICE isn't set

If DD_SERVICE is set, only APM picks it up.

Behavior after:

Same if DD_SERVICE isn't set

If DD_SERVICE is set, both APM service name & DSM service name use it.

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0daaf53) 82.29% compared to head (28b2d41) 82.39%.

❗ Current head 28b2d41 differs from pull request most recent head 1643835. Consider uploading reports for the commit 1643835 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   82.29%   82.39%   +0.09%     
==========================================
  Files          13       13              
  Lines         887      886       -1     
==========================================
  Hits          730      730              
+ Misses        127      126       -1     
  Partials       30       30              

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