Make "Battery usage" accessible at any time

Before this cl, user could go to "Battery usage" page only if
related app has battery usage. This cl breaks this rule so we
could open "Battery usage" without battery data.

Bug: 38497822
Test: RunSettingsRoboTests
Merged-In: Ic53c33b7dcbac82de58f31cf96e0bd8fa54e53ea
Change-Id: Ic53c33b7dcbac82de58f31cf96e0bd8fa54e53ea