Do not unregister sensors after a pulse

This generates unnecessary traffic to the system process
and SLPI. mDozeSensors.setListening(true) already makes
sure that any TriggerSensors will re re-registered.

Fixes: 126415281
Test: manual, look at logs
Change-Id: Ic7eea1f9c3dd1248dbb5fa38add70c1c2482120c