Fix: cpp-common/bt2c/logging.hpp: remove one definition of `BT_CPPLOGE_APPEND_CAUSE_A...

Fix: cpp-common/bt2c/logging.hpp: remove one definition of `BT_CPPLOGE_APPEND_CAUSE_AND_THROW_SPEC`

`BT_CPPLOGE_APPEND_CAUSE_AND_THROW_SPEC` has two identical definitions,
remove one.

Change-Id: Ia5b7caae53b65169081e9d8214896887fa062ad4
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12198
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>