flt.utils.muxer: remove `assume-absolute-clock-classes` param

flt.utils.muxer: remove `assume-absolute-clock-classes` param

It's a now a postcondition that all the messages of a given message
iterator have compatible clock classes. Thus the
`assume-absolute-clock-classes` parameter is useless as there is no more
need to force a muxer to accept possibly non-compatible clock classes
because we check that they are indeed all compatible.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I1efcd99abfd1da1d9a4b7c9c6962f898446d31d1
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2067
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Jonathan Rajotte Julien <jonathan.rajotte-julien@efficios.com>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>