Accessibility: Privacy: Improve the readability of the removed text in Privacy Policy Guide.

Per WCAG 2.0 guidelines, big chunks of italic text should be avoided for better accessibility.

Additionally, replace the legacy `.error` class for "You deactivated this plugin and may no longer need this policy" message with `.notice-info`.

Follow-up to [47147], [48116].

Props afercia, audrasjb.
See #47327, #44621.
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git-svn-id: https://core.svn.wordpress.org/trunk@47914 1a063a9b-81f0-0310-95a4-ce76da25c4cd