Hide chrome code requirement from I2P template

[GagandeepSingh20]

Fixes #6496

Summary

• Prevent the "Requires code in //chrome?" section from rendering for prototype / I2P intent emails.
• Updated the prototype intent preview golden output to match the template change.

Testing

• Ran git diff --check
• Verified Requires code in //chrome? is removed from test_html_prototype_rendering.html
• Verified the section is still present in ship and origin trial golden outputs

Notes

• python3 -m pytest -q api/intents_api_test.py could not be run locally because pytest is not installed.
• python3 -m unittest api.intents_api_test -b could not be run locally because local Python dependencies such as flask are not installed.

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