生成线的代码：
self.path = [UIBezierPath bezierPath];

[self.path moveToPoint:from];
[self.path addLineToPoint:to];
self.pathLayer = [CAShapeLayer layer];
self.pathLayer.frame = containerView.bounds;
self.pathLayer.path = self.path.CGPath;
self.pathLayer.strokeColor = color.CGColor;
self.pathLayer.lineWidth = 2.0f;
self.pathLayer.lineJoin = kCALineJoinBevel;

NSMutableArray *ary = [NSMutableArray arrayWithArray:shapeLayers];
[ary addObject:self.pathLayer];
shapeLayers = [NSMutableArray arrayWithArray:ary];
[containerView.layer addSublayer:self.pathLayer];

如何将上述线删除，在画新线