Use standard CI build script

.gitlab-ci.yml

-stages:
-  - build_src
-  - build_pkg
-  - upload
-
-build:src:
-  stage: build_src
-  image: "ai/build:stretch"
-  script: "build-dsc"
-  artifacts:
-    paths:
-      - build-deb/
-
-build:pkg:
-  stage: build_pkg
-  image: "ai/build:stretch"
-  script: "build-deb"
-  dependencies:
-    - build:src
-  artifacts:
-    paths:
-      - output-deb/
-
-upload:ai3:
-  stage: upload
-  image: "ai/pkg:base"
-  script: "upload-packages --repository=ai3"
-  dependencies:
-    - build:pkg
+include: "https://git.autistici.org/ai3/build-deb/raw/master/ci-common.yml"