Elon Musk says Tesla will wind down Cybertruck production next year after years of persistently weak sales for a futuristic model once touted as a rival to legacy pickup trucks.The move is a major retreat from what has been one of Mr Musk's pet projects. Mr Musk said the move would let Tesla make more of the Cybercab, a robotic taxi he has made central to the automaker's autonomous-vehicle ambitions, but one that has yet to prove itself commercially.It has been a bruising week for Mr Musk, as his record political spending of nearly half a billion dollars yielded little in…