Revert "Implement APIGW Inferred Proxy Spans"

[PerfectSlayer]

This PR reverts #8336

The reverted PR has multiples issues:

• Design issue where context element and propagator dedicated to tracing landed on the common context component,
• Performance issues:
  • context extraction will be run multiple time when receiving a web request: one as part of context extraction, then every time a new span start,
  • collection allocation where the context item is simply a glorified key/value store (like baggage) for headers

The part of the code is also heavily interacting with some refactoring in progress (baggage support) that was started earlier by @mhlidd. We (the guild) will revert it for now as it still reverts nicely, and started some clean up pull requests #8795 by @mcculls and #8801 by @PerfectSlayer.

In addition, this feature should be implementable using a single context extraction pass, and a context element to store the inferred span. No sub-classing of the agent span would be needed, only the HTTP_DECORATOR would update both tracing and inferred active spans (if any).

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