Citroën is reviving one of its most famous cars as a sub-£15,000 electric city car. It looks like a nostalgia play, but it is really a response to a gap Europe’s carmakers left at the cheap end of the market, one that Chinese rivals are now moving quickly to fill. Citroën’s decision to bring back the 2CV as a cheap electric car is not really about nostalgia. It is a response to a gap that Europe’s carmakers left at the bottom of the market, and …