Refactored tests of Request::getTrustedProxies()

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This PR reorganizes the tests for the request trusted proxies as they were unreadable. In the process, I've also removed obsolete stuff and changed the order returned by `Request::getClientIps()` (not a BC break as this method was added in 2.3 -- see #7612).