src.ctf.fs: make ctf_fs_component::trace a unique_ptr

src.ctf.fs: make ctf_fs_component::trace a unique_ptr

Define ctf_fs_trace::UP to be a unique_ptr type with a deleter that
calls ctf_fs_trace_destroy (the custom deleter will go away once
ctf_fs_trace is properly destructible).  Change ctf_fs_component::trace
to be of this type.

Change-Id: Iaf8111922b320781d7e9333bcdc5db129192509d
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8240
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>