cpp-common/bt2: don't use wrap in bindings code

cpp-common/bt2: don't use wrap in bindings code

Using `wrap()` in bindings code causes cyclic include problems, stop
using it.

For instance, we want to add `wrap(bt_graph *)`, so `wrap.hpp` needs to
include `graph.hpp`.  But `graph.hpp` currently uses and includes
`wrap.hpp`.

Change-Id: I5b7005617ed38eb791edf5802a05a8a8dd3115fd
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12045
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>