collide: restore missing CollisionTraverser.showCollisions()

This was an accidental regression in e48a40abad5399c7c3a0abffe1dfb3256b9a2317 which unexposed CollisionVisualizer and therefore caused this method to no longer be wrapped by Interrogate.

panda/src/collide/collisionTraverser.cxx

@@ -399,7 +399,7 @@ set_recorder(CollisionRecorder *recorder) {
  * should be any node in the scene graph; typically, the top node (e.g.
  * render).  The CollisionVisualizer will be attached to this node.
  */
-CollisionVisualizer *CollisionTraverser::
+PandaNode *CollisionTraverser::
 show_collisions(const NodePath &root) {
 #ifdef DO_COLLISION_RECORDING
   hide_collisions();

panda/src/collide/collisionTraverser.h

@@ -72,7 +72,7 @@ PUBLISHED:
   MAKE_PROPERTY2(recorder, has_recorder, get_recorder,
                            set_recorder, clear_recorder);
 
-  CollisionVisualizer *show_collisions(const NodePath &root);
+  PandaNode *show_collisions(const NodePath &root);
   void hide_collisions();
 #endif  // DO_COLLISION_RECORDING