Update the "Remove project avatar" modal's button

What does this MR do and why?

This changes the "Remove project avatar" modal's primary button by:

• Setting the variant to danger as the action is irreversible.
• Changing the label to Remove avatar for more clarity.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the bootstrap_confirmation_modals feature flag.

   Feature.enable(:bootstrap_confirmation_modals)

2. Go to any project's general settings.
3. Add an avatar if it doesn't have one already.
4. Click on Remove avatar.

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.

Related to #344166 (closed)