Remove mutated copy of `AnalogSignal.splice()`.
Remove mutated copy of `AnalogSignal.splice()`.

Ironically, this seems to have been spliced in during a merge

apdavison/python-neo,INM-6/python-neo,samuelgarcia/python-neo,JuliaSprenger/python-neo,rgerkin/python-neo,NeuralEnsemble/python-neo