Remove deprecated `tag` prop from AccordionToggleIcon

[bhaskarpraveen]

What

As part of our future breaking changes, remove the deprecated tag prop from the AccordionToggleIcon component.

Why

• Simplifies the component API
• Cleans up dead code ahead of the next major release

Acceptance Criteria

• tag?: never is removed from the AccordionToggleIconProperties type
• No remaining references to tag in the component code
• Any demo or example in the workshop app that mentioned tag= is updated or removed
• All tests pass and coverage stays at 100%
• Workshop examples still render correctly without errors