Don't let TouchInteractionService get created for the System user

In HSUM mode, the system user and the main user both had TouchInteractionServices being
created. These would create 2 Taskbar windows leading to the 2 back
arrows showing up. In this change, we avoid creating a
TouchInteractionService for the System user as it is not intended to be
there.

Fix: 341047445
Test: Factory reset a device with HSUM build and ensure only one back
arrow shows up. Ensure that non-HSUM builds are unaffected.
Flag: EXEMPT bugfix

Change-Id: I81574f198717d3e1e6c853bbf40fe1de43737f71