bullet: Streamline bundling, remove extraneous src/ folder

Document version and how to extract sources in thirdparty/README.md.
Drop unnecessary CMake and Premake files.
Simplify SCsub, drop unused one.

thirdparty/bullet/Bullet3OpenCL/RigidBody/kernels/updateAabbsKernel.cl

@@ -0,0 +1,22 @@
+
+
+#include "Bullet3Collision/NarrowPhaseCollision/shared/b3UpdateAabbs.h"
+
+
+__kernel void initializeGpuAabbsFull(  const int numNodes, __global b3RigidBodyData_t* gBodies,__global b3Collidable_t* collidables, __global b3Aabb_t* plocalShapeAABB, __global b3Aabb_t* pAABB)
+{
+	int nodeID = get_global_id(0);
+	if( nodeID < numNodes )
+	{
+		b3ComputeWorldAabb(nodeID, gBodies, collidables, plocalShapeAABB,pAABB);
+	}
+}
+
+__kernel void clearOverlappingPairsKernel(  __global int4* pairs, int numPairs)
+{
+	int pairId = get_global_id(0);
+	if( pairId< numPairs )
+	{
+		pairs[pairId].z = 0xffffffff;
+	}
+}