revert r6895, it perturbs measurements

tools/starpu_calibrate_bus.c

@@ -78,12 +78,9 @@ int main(int argc, char **argv)
 
 	parse_args(argc, argv);
 
-	if (starpu_init(NULL) == -ENODEV)
-		return 0; /* Nothing to calibrate, so this is a success :) */
+	/* Note: do not initialize StarPU, to avoid perturbing measurements.  */
 
 	starpu_force_bus_sampling();
 
-	starpu_shutdown();
-
 	return 0;
 }