Fix testGetDeviceOwnerDisclosure test case fail

- Remove the learn more part which already include in the FooterPreference.

Fixes: 190889944
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.enterprise.EnterprisePrivacyFeatureProviderImplTest
Change-Id: Ia6b7962019a3ec30b72ca6d64159811ab98fc13b