fix(avatar): remove avatar border on ionic theme (#30045)

Issue number: internal

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## What is the current behavior?

- Removed avatar border with ionic theme, to align with UX/UI design.
- Updated snapshots

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

[Avatar Ionic
Sample](https://ionic-framework-nimqjtxw7-ionic1.vercel.app/src/components/avatar/test/shape?ionic:theme=ionic)