Remove prev/next buttons on issues and merge requests
What does this MR do?
Remove prev/next buttons on issues and merge requests sidebar
Are there points in the code the reviewer needs to double check?
No
Why was this MR needed?
The buttons were rarely used and added at least 1 query each on every page load which we could live without.
What are the relevant issue numbers?
Screenshots (if relevant)
Below is how it looks. Not sure if it's too much empty space. #17697 (moved) discusses a possible substitute for what to put there.
