Defer trace context extraction to ddtrace.

[purple4reina]

SVLS-3936

What does this PR do?

Instead of manually extracting trace context from inbound payloads, defer that responsibility to dd-trace-py. This allows us to support w3c trace context headers.

Motivation

Support for w3c trace context headers, why implement this extraction when the tracer has already done it.

Testing Guidelines

Additional Notes

Types of Changes

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

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• This PR contains breaking changes that are documented in the description
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