tools lib traceevent: Use USECS_PER_SEC instead of hardcoded number

Instead of using 1000000, use the define in time64.h instead.

Also remove the the duplicate defines for NSECS_PER_SEC.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20161121114149.67111981@gandalf.local.home


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>