去掉obi，使用自写绳索

Assets/Obi/Scripts/Common/DataStructures/BVH/BIHNode.cs

@@ -1,25 +0,0 @@
-using System;
-
-namespace Obi
-{
-    public struct BIHNode
-    {
-        public int firstChild;     /**< index of the first child node. The second one is right after the first.*/
-        public int start;          /**< index of the first element in this node.*/
-        public int count;          /**< amount of elements in this node.*/
-
-        public int axis;           /**< axis of the split plane (0,1,2 = x,y,z)*/
-        public float min;          /**< minimum split plane*/
-        public float max;          /**< maximum split plane*/
-
-        public BIHNode(int start, int count)
-        {
-            firstChild = -1;
-            this.start = start;
-            this.count = count;
-            axis = 0;
-            min = float.MinValue;
-            max = float.MaxValue;
-        }
-    }
-}