selftests/nolibc: remove test gettimeofday_null

gettimeofday() is not guaranteed by posix to handle a NULL value as first
argument gracefully.
On glibc for example it crashes. (When not going through the vdso)

Link: https://lore.kernel.org/lkml/96f1134d-ce6e-4d82-ae00-1cd4038809c4@t-8ch.de/


Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>