Notice: Drop the props @wordpress/ui removed to unblock the dependency update

[Nikschavan]

Fixes N/A

Proposed changes

• The @wordpress/ui update in Update wordpress monorepo #53004 picks up UI: Remove automatic Notice announcements WordPress/gutenberg#82737, which removed the automatic announcement from Notice.Root together with its spokenMessage and politeness props. That fails Update wordpress monorepo #53004 on "Type checking", and on "JS tests" through the React unknown-prop console error and the tests that assert an announcement. Eslint: adopt @wordpress/use-recommended-components #48487 is based on Update wordpress monorepo #53004, so it is blocked by the same failures.
• Remove spokenMessage and politeness from every Notice.Root, along with the comments that explained them. The two Publicize notices use the @wordpress/components Notice, whose API did not change, so they should be handled separately.
• Where an existing test asserts an announcement on a dynamic notice, restore what Notice.Root used to do: call speak() when the message changes, assertive for errors and polite otherwise. This covers Backup (QueryError and the restore warnings), the Boost Overview errors, and the Premium Analytics PageNotice, StaleDataNotice and SectionSyncNotice failure. Boost and Premium Analytics now depend on @wordpress/a11y for this.
• Following the migration guide, static notices are not announced. The Boost "Website is not publicly available" notice and the SectionSyncNotice syncing and pending states are now silent, and their tests check for that.
• This PR is kept small on purpose, so Update wordpress monorepo #53004 can merge. Choosing politeness by urgency rather than intent, moving speak() into the handlers that own each update, leaving technical details out of QueryError, and announcing the notices that are now silent are left for a follow-up against trunk.

Related product discussion/links

• Notice announcements migration guide: https://wordpress.github.io/gutenberg/?path=/docs/design-system-components-notice-announcements--docs#migrating-existing-notices
• p1791538827887519/1790796321.030479-slack-CDLH4C1UZ

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

No.

Testing instructions

• Nothing to test by hand for most of this. On this PR, "Type checking" should show no Notice.Root errors, and "JS tests" should have no spokenMessage console errors or failing announcement tests, where Update wordpress monorepo #53004 has both.
• To hear an announcement, check out this branch, build Boost (jp build plugins/boost --deps), and open Jetpack → Boost with a screen reader running. Make the speed score request fail (for example, block requests matching speed-scores in the browser's network tools, then reload) and confirm that "Failed to load speed scores" is announced once.
• I ran typecheck and the JS tests for Backup, Boost, Newsletter, Premium Analytics, Search, VideoPress and the Jetpack AI screens. I did not test speech in a browser.

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