Recovery: Fix backup change detection not working in rust

[BillCarsonFr]

Fixes https://github.com/element-hq/element-web/issues/26792

React sdk was still making usage of client#getKeyBackupEnabled() that is deprecated and failing in rust stack. That would cause the following dialog to not show up:

• When the backup is deleted from another session

• When backup is reset from another session

Checklist

• [ ] Tests written for new code (and old code if feasible)
• [ ] Linter and other CI checks pass
• [ ] Sign-off given on the changes (see CONTRIBUTING.md)

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Here's what your changelog entry will look like:

🐛 Bug Fixes

• Recovery: Fix backup change detection not working in rust (#12160). Fixes element-hq/element-web#26792.