Fix wrong path checks in monitor (bug 1013865)

We don't need to check upon those paths:

- `user_media_path('uploads')` is the old `settings.MEDIA_ROOT` (which is the root of all the `user_media_path`)
- `settings.REVIEWER_ATTACHMENTS_PATH` is already checked by `user_media_path('reviewer_attachments')`, which is the proper way to get the path