Remove copy_back from Python bindings and mj_copyBack from the C API.

PiperOrigin-RevId: 687377331
Change-Id: I355493d92857418b08b5aa90ea38cebe5c475314

src/xml/xml_base.cc

@@ -21,6 +21,7 @@
 #include <string>
 #include <vector>
 
+#include <mujoco/mjmodel.h>
 #include <mujoco/mjspec.h>
 #include "xml/xml_util.h"
 #include "tinyxml2.h"
@@ -43,7 +44,7 @@ mjXBase::mjXBase() {
 
 
 // set model field
-void mjXBase::SetModel(const mjSpec* _model) {
+void mjXBase::SetModel(const mjSpec* _model, const mjModel* m) {
   spec = (mjSpec*)_model;
 }