meta-agl-bsp: remove old Xen recipes

meta-agl-bsp: remove old Xen recipes

Remove old Xen recipes and bbappends, as they have not been maintained
in a long time, and are no longer buildable / relevant after the upgrade
to YP scarthgap.

Bug-AGL: SPEC-5202

Change-Id: I5ba07585213836ab8f4e1bd7358dc55e52a3c71e
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/30099
ci-image-build: Jenkins Job builder account
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>