tmf: Update XML trace stub to use ns directly

tmf: Update XML trace stub to use ns directly

Now that custom parsers support nanoseconds timestamps, the custom XML trace
stub does not need to convert the timestamps to nanoseconds anymore, it can
be defined directly in the XML trace definition.

Change-Id: I2791b350c303bb82df9f83f0cabbb663e1166a75
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/88513
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>