Consider removing charting/StoreSeries for 2.0

[kfranqueiro]

Dojo 2.0 will most likely ultimately take a fresh look at charting and feature store support as a first-class citizen, as opposed to dojox/charting in which store support was largely implemented as an afterthought. As such, it probably makes sense to just nuke the StoreSeries module.

As it stands, we had to do some not-very-nice things in #145 to get its tests to cooperate when switching to promises with next-turn resolution.

PS: we probably should remember to prune from the docs as well, while we're at it.