Disable allowMerchantAIAPIKey flag in all builds

[iamgabrielma]

Description

This PR disables the allowMerchantAIAPIKey flag for the time being so it doesn’t render just an empty view in dev builds while we prioritize the project.

Testing information

• Run the app
• Go to menu
• Observe how "AI settings" row does not appear.

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr15421-d8bf028
	Version	22.0
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	d8bf028
	App Center Build	WooCommerce - Prototype Builds #13413

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[itsmeichigo]