frontend: battery-indicator: total consumed Wh are inaccurate

[ES-Alexander]

Current behaviour

It's hard enough to get accurate energy consumption estimates from the autopilot / battery monitor (when it's trying to calculate them) - doing our own calculations just from the telemetry (per #1370) seems more problematic than helpful.

@vshie has mentioned the calculated values do not seem to make sense.

Expected or desired behaviour

Cockpit should only display energy consumption values provided from an external source (e.g. via MAVLink). If no such value is provided then the energy usage should be either be specified as unknown (e.g. -- or ?), or unspecified (e.g. when configured to toggle between voltage+current and power+consumption, just toggle between the current and power and keep the voltage at the top).

Prerequisites

• [X] I have checked to make sure that a similar request has not already been filed or fixed.

[rafaellehmkuhl]

Yeah... it makes sense. We are integrating very spaced values over long periods of times. I liked the idea of toggling between current and power. Will do it.