fix pseudonyms API doc optional fields

- pseudonyms "List" API has a redundant user[id]
- pseudonyms "Create" API needs 'password' and 'sis_user_id' marked Optional
- pseudonyms "Edit" API needs 'unique_id', 'password', 'sis_user_id' marked Optional

Fixes SIS-354

Change-Id: Id03f1a813d43a9a2f75b7f1ea4d44e87931f84ec
Reviewed-on: https://gerrit.instructure.com/37595
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Eric Adams <eadams@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>