Check the current user in the system server for SensorPrivacyManager

Instead of querying for the current user application side we can just
pass UserHandle.CURRENT_USER, this eliminates an IPC and the need for
INTERACT_ACCROSS_USERS permission which should not be needed for these
APIs.

Test: CtsSensorPrivacyTestCases
Bug: 194806109
Change-Id: I3a0aed0c403338aaebdfb4e2791a84b4e7e3cb3a