Revert "Add new battery_charged event type reason"

[marie-x]

Reverts #237

[Retzoh]

Hi @karcass , sorry for returning to this PR later on but why was the battery_charged transition removed? It actually makes a lot of sense in the carsharing context.

[marie-x]

I don't recall. I think @hunterowens had some concern about it. Probably should have written that reasoning down! I'd be fine with re-adding battery_charged as a transition from unavailable to available.

[thekaveman]

I think at least some of the reasoning was related to how it wasn't totally clear how new modes (specifically carshare) are represented in MDS. I think we have a better idea now after #336.