Exempt the system from TARE restrictions.

Since the system needs to operate in order for everything else to
function, make sure the system is always given the go ahead to do
whatever work it wants.

Also stop saving transactions with a delta of 0 in order to reduce
memory usage.

Bug: 158300259
Test: Check dumpsys
Change-Id: Ifc90cd0f0813f82bd99c0fe90beca252b69714df