Resolve "Update copy for the remove topic avatar modal"

What does this MR do and why?

Update the copy being displayed in the remove topic avatar modal.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Browse to admin > overview > topics
• Add a topic (if one doesn't exists)
• Edit the topic
• Add an avatar
• Save changes
• Remove the 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 #356140 (closed)