kleaf: //build/kleaf -> //build/kernel/kleaf.

This is part of the build/ -> build/kernel migration.
The //build/kleaf package is deprecated. Use //build/kernel/kleaf
instead.

Test: TH
Bug: 217630659
Signed-off-by: Yifan Hong <elsk@google.com>
Change-Id: I914d7444c43bd26b1f5f04b9760ddf1b38d6214c