selftests/arm64: remove ARRAY_SIZE define from vec-syscfg.c

ARRAY_SIZE is defined in several selftests. Remove definitions from
individual test files and include header file for the define instead.
ARRAY_SIZE define is added in a separate patch to prepare for this
change.

Remove ARRAY_SIZE from vec-syscfg.c and pickup the one defined in
kselftest.h.
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/arm64/fp/vec-syscfg.c

@@ -21,8 +21,6 @@
 #include "../../kselftest.h"
 #include "rdvl.h"
 
-#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
-
 #define ARCH_MIN_VL SVE_VL_MIN
 
 struct vec_data {