ctf: remove ctf_fs_trace::name

ctf: remove ctf_fs_trace::name

Now that we don't report the name of CTF traces in
`babeltrace.trace-info`, it is no longer useful to invent a name for
each trace.  So remove the ctf_fs_trace::name field, and everything
related to it.

Note that the name set on the bt_trace (in set_trace_name) does not
depend on this field.

Change-Id: Ia1d3e917e7b1c553c0da0c8365cda9ec600c854b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1991
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>