SystemUI: Remove unused method SecurityController#getDeviceOwnerType()

Following http://ag/32928330 ("Remove ADD_ISFINANCED_DEVICE_FLAG") and
http://ag/34817750 ("Switch to SecurityController#isFinancedDevice()"),
SecurityController#getDeviceOwnerType() is no longer used.  Remove it
from the interface, remove all implementations and mocking of it, and
remove the mocking of DevicePolicyManager#getDeviceOwnerType() which was
needed only for SecurityControllerImpl#getDeviceOwnerType().

Also change KeyguardIndicationControllerBaseTest#DEVICE_OWNER_COMPONENT
from protected to private, since this change removes the only use of it
from a subclass (KeyguardIndicationControllerTest).

Bug: 259908270
Test: m; m SystemUITests
Flag: EXEMPT removing unused code following a flag removal
Change-Id: Iaa989969b05391253d910ef5a1387ebee2fc18be