sink.text.pretty: remove message iterator inactivity message logging

sink.text.pretty: remove message iterator inactivity message logging

This is not the role of this component class. A detailed component
class, `sink.text.details`, shows all the messages.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Ic01b766a81fd622fc768d71f70aec4b4a136c3d0
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1444
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>