removed unused _clearPaint from bar_chart_painter.dart
removed unused _clearPaint from bar_chart_painter.dart

imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart,imaNNeoFighT/fl_chart