[doc] Restore banner's original content

[jcalcaben]

Description

This PR will remove the migration message and restore the message to the previous one.

Related Issue

Closes #ISSUE_NUMBER.

Verification Steps

1. Navigate to the pwa-devdocs directory
2. Build the preview HTML: npm run develop
3. Verify the blue banner is back with original message.

Screenshots / Screen Captures (if appropriate)

n/a

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[supernova-at]

Added the hold label because this should not be merged until after the repository is moved.