Remove unused images

What does this MR do?

Remove unused images

bg-header.png
bg_fallback.png
chosen-sprite.png
diff_note_add.png
icon-search.png
icon_sprite.png
images.png
move.png
progress_bar.gif
slider_handles.png

Are there points in the code the reviewer needs to double check?

Just need to check if the images are still being used 😄

Why was this MR needed?

To reduce the technical debt of the project

What are the relevant issue numbers?

Closes #20499 (closed)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together