[ci/cloud-deploy] Skip CDN assets build (elastic#170959)

The cloud deploy image is created using a resume build, relying on an
existing kibana.tar.gz. The source files needed to build CDN assets are
not available and this step is not needed.

.buildkite/scripts/steps/cloud/build_and_deploy.sh

@@ -37,6 +37,7 @@ else
     --skip-generic-folders \
     --skip-platform-folders \
     --skip-archives \
+    --skip-cdn-assets \
     --docker-images \
     --docker-tag-qualifier="$GIT_COMMIT" \
     --docker-push \