Remove some duplicate tests and fix some typos

What does this MR do?

This MR cleans up some duplicate API integration tests, updates some test descriptions and fixes some typos.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/50390

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the [merge request performance guidelines](https://docs.gitlab.com/ee/development/merge_request_performance_guidelines.html)
• Conforms to the style guides
• Conforms to the database guides