list_sort.c's core code should only change on sync with Linux, so we
don't really need separate testing code. The code doesn't compile as
we neither have a CONFIG_TEST_LIST_SORT symbol nor do we have a
<linux/random.h> header. Remove it.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>