Help Center: guard helpCenterData against redeclaration

[escapemanuele]

Part of https://linear.app/a8c/issue/DOTCOM-16285/remove-helpcenterfeatureflags
Fixes https://linear.app/a8c/issue/DOTCOM-16282/fix-helpcenterfeatureflags-redeclaration-error

Summary

• Remove the unused helpCenterFeatureFlags inline script and its associated is_next_steps_tutorial_enabled() method, which was causing SyntaxError: redeclaration of const helpCenterFeatureFlags in CIAB admin (DOTCOM-16282).
• Guard helpCenterData with a typeof check and var to prevent the same redeclaration issue.

The root cause is that in CIAB admin, the load-assets package re-injects inline scripts that were already output in the initial page HTML. Since const cannot be redeclared in the same scope, the browser throws a SyntaxError.

Also the feature flags global is no longer consumed, so it can be removed entirely. helpCenterData is still needed but is now safe against double-injection.

Does this pull request change what data or activity we track or use?

No

Testing instructions

• Verify Help Center still loads correctly on Simple/Atomic sites.
• Verify Help Center still loads correctly in CIAB admin without console errors.
• Verify the helpCenterFeatureFlags redeclaration error no longer appears in PostHog.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (WordPress.com Site Helper), and enable the fix/help-center-feature-flags-redeclaration branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/help-center-feature-flags-redeclaration

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/jetpack-mu-wpcom/src/features/help-center/class-help-center.php	0/338 (0.00%)	0.00%	-14 💚

Full summary · PHP report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}