Clean up redirect checks in OAuth2_Storage_Client, refs T309

Summary:
- only strip domain for the ushahidiui client
- simplify stripping

Test Plan:
```
bin/behat -f progress -c application/tests/behat.yml application/tests/features/api.oauth.feature
```

Reviewers: vladimir, rjmackay

Reviewed By: rjmackay

Subscribers: aMoniker, srutto

Maniphest Tasks: T309

Differential Revision: https://phabricator.ushahidi.com/D395