Remove display inline-block from avatar

What does this MR do and why?

This CSS cleanup allows clients to override styles of the avatars more easily by removing CSS that is already part of the avatar via inline-flex.

Screenshots or screen recordings

As we have display: inline-block; overriding an display: inline-flex style no difference is visible in regular usages of the avatar.

How to set up and validate locally

1. Visit a page such an issue page e.g. http://gdk.test:3000/twitter/Typeahead.Js/-/issues/12
2. Add comments in a thread, and confirm the layout is correct.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.