Fix enhanced estimate discharge text showing while charging

In the PowerUsageAdvanced screen the text showing whether your time
remaining information is enhanced or not should not show when the
device is plugged in. This CL fixes a bug in that logic that would
show the text when it wasn't supposed to.

Test: robotests still pass, manual verification
Bug: 63176050
Change-Id: I33fb31671cd9c29aed20483301e51ae1ded1f1b6