chore: remove leftover esbuild and webpack examples and references

[mellyeliu]

What changed / motivation ?

Just removing some legacy examples and references that rely on #954

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

[github-actions]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.

[email protected] size:compare
node size/compare.js /tmp/tmp.Vv7XsKW1m8 /tmp/tmp.hOo3aP01yX

Results	Base	Patch	Ratio
stylex/lib/stylex.js
· compressed	985	985	1.00
· minified	3,154	3,154	1.00
stylex/lib/StyleXSheet.js
· compressed	1,266	1,266	1.00
· minified	3,776	3,776	1.00
benchmarks/size/.build/bundle.js
· compressed	537,611	537,611	1.00
· minified	7,435,904	7,435,904	1.00
benchmarks/size/.build/stylex.css
· compressed	100,609	100,609	1.00
· minified	755,721	755,721	1.00