BatteryStats: Pull subsystem stats from Power Stats Service

Also remove redundant PlatformIdle stats section from history details

Bug: 173132005
Bug: 178315485
Test: Ran device to drain battery then checked dumpsys batterystats
Test: Verified that Historian could correctly parse the bugreport
Change-Id: I65c1824695dd026231f83664b00f72912dee2164