Rename "default beginning/end CS" -> "beginning/end default CS"

Rename "default beginning/end CS" -> "beginning/end default CS"

Because the target is the "default clock", it makes more sense to keep
those words together and have the beginning/end adjective outside.

Suggested-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I9fdd32c6acefc51b63b322dc41470c50b9226dfa
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1369
Tested-by: jenkins
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>