fix compile errors with older bullet versions

panda/src/bullet/bulletContactResult.cxx

@@ -131,9 +131,6 @@ addSingleResult(btManifoldPoint &mp,
                 const btCollisionObject *obj0, int part_id0, int idx0,
                 const btCollisionObject *obj1, int part_id1, int idx1) {
 
-  const btCollisionObject *obj0 = wrap0->getCollisionObject();
-  const btCollisionObject *obj1 = wrap1->getCollisionObject();
-
   BulletContact contact;
 
   contact._mp = BulletManifoldPoint(mp);

panda/src/bullet/bulletWorld.cxx

@@ -764,10 +764,11 @@ contact_test(PandaNode *node, bool use_filter) const {
   BulletContactResult cb;
 
   if (obj) {
-
+#if BT_BULLET_VERSION >= 281
     if (use_filter) {
       cb.use_filter(_filter_cb, obj->getBroadphaseHandle());
     }
+#endif
 
     _world->contactTest(obj, cb);
   }