armv8r64-extras/zephyr: remove the inclusion of zephyr .inc file

The recent patch
https://git.yoctoproject.org/meta-zephyr/commit/?h=langdale&id=2a81a45bfbd42bb1995f66a6f8e38151fee95428


in meta-zephyr langdale branch changed the inclusion of the Zephyr
version-specific .inc file, it doesn't use the local include now,
so it is unnecessary to include it in meta-armv8r64-extras.

Issue-Id: SCM-5560
Signed-off-by: Jiacheng Tang <jiacheng.tang@arm.com>
Change-Id: I63f1f544acad16c2f5410a49cd2d6b04efd0cb16