Let image inherit architecture

Since the image architecture will probably never be used for anything in
Nest, just let it take on whatever Gentoo sets for their builds.  Good
enough.

.gitlab-ci.yml

@@ -14,7 +14,6 @@ default:
   script: &script
     - 'mkdir debug'
     - 'buildah bud --pull --squash
-                   --arch "$GENTOO_ARCH"
                    --security-opt seccomp=unconfined
                    --build-arg GENTOO_STAGE3_TAG="$GENTOO_ARCH"
                    --build-arg EMERGE_DEFAULT_OPTS="${CI_HOST_EMERGE_DEFAULT_OPTS} --usepkg"
@@ -24,7 +23,7 @@ default:
                    -v "${PWD}/debug:/usr/lib/debug"
                    -v /nest:/nest
                    -t "${CI_REGISTRY_IMAGE}:${CPU}" .'
-    - 'buildah bud --arch "$GENTOO_ARCH" -t "${CI_REGISTRY_IMAGE}/debug:${CPU}" -f Containerfile.debug .'
+    - 'buildah bud -t "${CI_REGISTRY_IMAGE}/debug:${CPU}" -f Containerfile.debug .'
     - 'buildah push "${CI_REGISTRY_IMAGE}:${CPU}"'
     - 'buildah push "${CI_REGISTRY_IMAGE}/debug:${CPU}"'