Do not show work profile strings for parent-managed enrollment

Work profiles and parental management both utilize the
DevicePolicyManager KEYGUARD_DISABLE_* flags. This CL ensures that
work profile strings are only shown for work profiles, and not
parent-managed devices.

Bug: 196060286
Bug: 196443744
Test: Set up child account, then enroll from Settings > Security
Change-Id: Ib5ed1d63dd5d58ac64caf30010e340ac7784c38f