Hotfix: Cleaning up feature flags + banner cards

[internetisaiah]

Why are you making this change? (required)

The platform_wide directory has been decommissioned, but these docs may have accidentally re-added it to the repo. I have also applied some style changes, to better match the work going on here: #8273.

Note: in a future PR, i will rename platform_integration_guides to platforms, which hopefully makes the now-missing platform_wide directory make more intuitive sense.

Related PRs, issues, or features (optional)

• Changes have also been made to the other repo. Merge both simultaneously so the cross-references work appropriately.

Feature release date (optional)

• N/A

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[bre-fitzgerald]

Lgtm with a few minor comments!