Remove users#show.json completely

What does this MR do?

Removes users#show.json completely, which was deprecated in !48712 (merged) in %13.7.

Screenshots (strongly suggested)

n/a

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides
• Separation of EE specific content

Closes #289972 (closed)