docs: remove DUT kernel version with broken link

The DUT kernel version link is broken. Actually users don't need
to use specific kernel version to run dataplane stack.

Signed-off-by: Liangxing Wang <liangxing.wang@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>
Change-Id: Iad84af6b1ac58742dfd7ffe281448b7520246eb7