Remove outdated dd-trace-py configuration instructions

[brett0000FF]

What does this PR do? What is the motivation?

• The tracer.configure() examples in the main Python tracing doc used parameters (hostname, port) that were removed in dd-trace-py v3.
• This was misleading for customers performing a fresh installation and resulted in a support ticket.
• This change removes the deprecated examples and updates the section to recommend configuring via environment variables.

Related, adding v3 migration guide in a separate PR: #30246

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/brett.blue/DOCS-11383/tracing/trace_collection/automatic_instrumentation/dd_libraries/python