feat: remove zisiEsbuildDynamicImports feature flag

[eduardoboucas]

- Summary

Removes a feature flag that is no longer used since netlify/build#3638.

- Test plan

N/A

- A picture of a cute animal (not mandatory but encouraged)

[github-actions]

📊 Benchmark results

Comparing with 5798771

Package size: 353 MB

⬇️ 0.00% decrease vs. 5798771

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└───┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴──>
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Legend

• T-28 (5798771): 353 MB
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• T-14 (f94cd3b): 353 MB
• T-13 (abd9c66): 352 MB
• T-12 (483a3fc): 352 MB
• T-11 (e05ac4f): 352 MB
• T-10 (631423c): 352 MB
• T-9 (03a8d1e): 352 MB
• T-8 (92cfa0a): 352 MB
• T-7 (29e2e3c): 352 MB
• T-6 (d929073): 352 MB
• T-5 (6e7e4ea): 352 MB
• T-4 (7ffb922): 352 MB
• T-3 (604e58a): 352 MB
• T-2 (23469be): 352 MB
• T-1 (863b20c): 352 MB
• T (current commit): 353 MB