ubsan: Remove vla bound checks.

The kernel the kernel is built with -Wvla for some time, so is not
supposed to have any variable length arrays.  Remove vla bounds checking
from ubsan since it's useless now.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>