Keep EnterprisePrivacySettingsActivity always enabled

The existing code checks during Settings startup whether the device is
managed. If it is not, EnterprisePrivacySettingsActivity is disabled.
If the device then becomes managed, Settings will not notice until
the next restart, causing any attempt to launch this Activity via an
Intent to crash.

This CL changes things so that the Activity is always enabled but
simply does nothing when launched on a non-managed device.

Bug: 34122104
Test: Integration test coming in a separate CL
Change-Id: I0a1dfcb41b405d981309696d97678df6787b4f72
(cherry picked from commit 92d25fb5)