This changes varobj_item::value to be a value_ref_ptr, removing some
manual management.
gdb/ChangeLog
2020-12-11 Tom Tromey <tom@tromey.com>
* varobj.c (install_dynamic_child, varobj_clear_saved_item)
(update_dynamic_varobj_children, create_child)
(create_child_with_value): Update.
* varobj-iter.h (struct varobj_item) <value>: Now a
value_ref_ptr.
* python/py-varobj.c (py_varobj_iter::next): Call release_value.