lib: mark bt_common_assert_failed as hidden

lib: mark bt_common_assert_failed as hidden

I noticed that the bt_common_assert_failed symbol was exported.  This is
not desirable, as it's not part of the API, so mark it with BT_HIDDEN.

As a consequence, a bunch of small tests that use BT_ASSERT miss this
symbol, as they were getting it from libbabeltrace2.  Make them depend
on libbabeltrace2-common (and libbabeltrace2-logging) directly to fix
that.

Change-Id: I25ab69e7df08f508389f5c9c3db5571ee7b06d7b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2402
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>