fix(CallView): remove shadow of avatars

[DorraJaouad]

☑️ Resolves

• Shadows are used only for elements on top of other elements, like menus/autocomplete

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[Antreesy]

Saw also box-shadow on Contact.vue component, not sure if needed there.
But fine for now

[DorraJaouad]

Saw also box-shadow on Contact.vue component, not sure if needed there.

(in a follow up) It's used to aesthetic purposes, we usually use outlined border on hover and focus (like polls). Maybe switch to that style too?

[DorraJaouad]

/backport to stable30