internal/telemetry: revert hostname.Get() -> os.Hostname()

[eliottness]

What does this PR do?

Motivation

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

Unsure? Have a question? Request a review!

[datadog-datadog-prod-us1]

Datadog Report

Branch report: eliottness/revert-hostname-telemetry
Commit report: 104b869
Test service: dd-trace-go

✅ 0 Failed, 5189 Passed, 72 Skipped, 2m 39.66s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-17 16:41:15

Comparing candidate commit 278b888 in PR branch eliottness/revert-hostname-telemetry with baseline commit 382c311 in branch main.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 57 metrics, 0 unstable metrics.

scenario:BenchmarkSetTagMetric-24

• 🟥 execution_time [+2.656ns; +5.144ns] or [+2.239%; +4.337%]

scenario:BenchmarkSetTagStringPtr-24

• 🟥 execution_time [+5.388ns; +9.552ns] or [+3.147%; +5.579%]