chore: remove adding meta from context in start_span

[ZStriker19]

Checklist

• [ ] Change(s) are motivated and described in the PR description.
• [ ] Testing strategy is described if automated tests are not included in the PR.
• [ ] Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• [ ] Change is maintainable (easy to change, telemetry, documentation).
• [ ] Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• [ ] Documentation is included (in-code, generated user docs, public corp docs).
• [ ] Backport labels are set (if applicable)

Reviewer Checklist

• [ ] Title is accurate.
• [ ] No unnecessary changes are introduced.
• [ ] Description motivates each change.
• [ ] Avoids breaking API changes unless absolutely necessary.
• [ ] Testing strategy adequately addresses listed risk(s).
• [ ] Change is maintainable (easy to change, telemetry, documentation).
• [ ] Release note makes sense to a user of the library.
• [ ] Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• [ ] Backport labels are set in a manner that is consistent with the release branch maintenance policy
• [ ] If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• [ ] This PR doesn't touch any of that.

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-01-03 20:43:17

Comparing candidate commit d2b290b30de69d2396a2d24ccf406522306471d9 in PR branch zachg/remove_unneeded_context_copy_to_spans with baseline commit 8d0a35e7682713e489c74c0b03e7fb35bf4f41ad in branch main.

Found 3 performance improvements and 0 performance regressions! Performance is the same for 192 metrics, 9 unstable metrics.

scenario:tracer-large

• 🟩 execution_time [-2.079ms; -1.715ms] or [-7.982%; -6.584%]

scenario:tracer-medium

• 🟩 execution_time [-176.167µs; -139.391µs] or [-6.846%; -5.417%]

scenario:tracer-small

• 🟩 execution_time [-18.675µs; -16.659µs] or [-6.162%; -5.497%]