fix: simplify trace implementation by removing unused code

[chenjiahan]

Summary

1. Remove entries > 0 check, because resolveLayer returns a non-empty string rather than an object.

- const entries = Object.entries(resolveLayer(filterValue));
- if (entries.length <= 0) return;

2. Remove duplicated mkdir, it has the same function as await ensureFileDir(traceOutput);.

- await fs.promises.mkdir(defaultOutputDirname);

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #10325 will not alter performance

_{Comparing simplify_trace_0511 (dfbbad1) with main (a9db9a8)}

Summary

✅ 11 untouched benchmarks