I am a bit disappointed about the Charts API!
One can add DataSeries but one can not remove a (list) of Series!
At least there is the possibility to set a new List of DataSeries (chart.getConfiguration().setSeries(new ArrayList<Series>());).
This indeed removes the old Series (and one can later add new ones) BUT: the legend of the old series is kept! 8-O
Thus, if I repeatedly add and remove DataSeries to a chart the legend keeps growing longer and longer. 
I would say this is clearly a bug!