Change: Remove permission manager

BREAKING CHANGE for developers: The `PermissionManager` has been removed. Permission management is now being handled by `CASL`. For more details on how it works please see the linked PR down below.

https://github.com/owncloud/web/pull/8431
https://github.com/owncloud/web/pull/8488
https://github.com/owncloud/web/pull/8509
