Replace mjs_detachBody and mjs_detachDefault with mjs_detach.

In a follow-up, mjs_detach will be changed to only remove without deleting an element.

PiperOrigin-RevId: 773637351
Change-Id: I9ee4d3584ba88ccc225591337cf036bab806e25c

src/user/user_model.h

@@ -232,9 +232,6 @@ class mjCModel : public mjCModel_, private mjSpec {
   // delete default and all descendants
   void RemoveDefault(mjCDef* def);
 
-  // detach subtree from model
-  void Detach(mjCBody* subtree);
-
   // API for access to model elements (outside tree)
   int NumObjects(mjtObj type);              // number of objects in specified list
   mjCBase* GetObject(mjtObj type, int id);  // pointer to specified object