Cleanup application settings spec

What does this MR do?

EE already includes specs for the ApplicationSettingsController, so ensure future changes will be easier to merge to EE.

Also check the EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1498

Why was this MR needed?

In 9-0-stable some conflicts are resolved, but not very clean. This will clean this up. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10070#note_25898584

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

@godfat Can you have a first look please? And also have a look at the EE MR please.

assigned to @godfat

@to1ne Yes but it's too late for me, so I'll look into it tomorrow. Thank you for fixing this!

mentioned in commit 4e1cebab

@godfat I still have to figure out the EE changes properly. So until they are complete, I'll reassign back to me.

assigned to @to1ne

@godfat I've finished the EE MR. Can you have a look at both please?

assigned to @godfat

@to1ne Thanks! CE looks good to me, now heading to the EE counterpart.

resolved all discussions

assigned to @smcgivern

approved this merge request

merged

mentioned in commit 5b84708d