Check that there are no pending keyframes while writing a spec.

This can happen when a body is detached without compiling or recompiling.

Also added error catching when trying to delete a body instead of detaching it.

Fixes #2327

PiperOrigin-RevId: 712526730
Change-Id: I4b48df83120fca12d475c85b3a54893841449653

src/user/user_model.cc

@@ -530,7 +530,6 @@ mjCModel& mjCModel::operator-=(const mjCBody& subtree) {
     ResetTreeLists();
   }
 
-  PointToLocal();
   return *this;
 }