code: def _trim_ser_count_by(self, plotArea, count):
          
          extra_sers = plotArea.sers[-count:]
          for ser in extra_sers:
              parent = ser.getparent()
              parent.remove(ser)
          extra_xCharts = [
              xChart for xChart in plotArea.iter_xCharts()
              if len(xChart.sers) == 0
          ]
          for xChart in extra_xCharts:
              parent = xChart.getparent()
              parent.remove(xChart)
docs: Remove the last *count* ser elements from *plotArea*. Any xChart
          elements having no ser child elements after trimming are also
          removed.