lib: internal: message.h: require logging

This patch makes the internal `message.h` require what it needs instead
of using the macros only if they exist. This makes it impossible to skip
logging in this header.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I2dd300931479a1d0752b6f90079c826324e19ce1
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1581
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>