selftests: vDSO: clock_getres: Drop unused include of err.h

Nothing from err.h is used.

Drop the include.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://lore.kernel.org/all/20250611-selftests-vdso-fixes-v3-2-e62e37a6bcf5@linutronix.de

Author: t-8ch

tools/testing/selftests/vDSO/vdso_test_clock_getres.c

@@ -13,7 +13,6 @@
 
 #define _GNU_SOURCE
 #include <elf.h>
-#include <err.h>
 #include <fcntl.h>
 #include <stdint.h>
 #include <stdio.h>