Delete issue description modal

What does this MR do and why?

This MR deletes the modal and associated code from the issue description, now that we no longer want to show anything in a modal from the issue description (!110552 (comment 1259620418))

Screenshots or screen recordings

How to set up and validate locally

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.