Remove the signature protection for sensor privacy permissions

Only a couple distinguished packages will need to hold these
permissions. We can grant via role for these cases.

Previously system ui was started assuming the system server was
initialized enough but the problem was that the role service may not
have finished granting all permissions. If we start sys ui after system
services have finished onUserStarting then we can _probably_ safely
assume the state of user 0 is initiallized.

Test: Wipe & reboot; dumpsys package com.android.systemui
Test: atest SystemUiTests
Bug: 184303952
Change-Id: I160ac8e0f2fbc36a76e8f2ee99d73e613ddc3c11