Restricts PersonalAppsSuspensionHelper.dump() to system user.

It calls a pm method that fails if called for a different user.
As this dump is mostly useful for system user anyways, we can just
ignore the other users (rather than changing the permission check in
the PM method).

Also fixed the userId passed to that method.

Test: adb shell dumpsys device_policy |grep -A 20 PersonalAppsSuspensionHelper # on automotive
Bug: 181238156

Change-Id: Ib416fe9be81a12f40b0b95bfe864d0b2c45efe0b