Build only on stretch, jessie is too old

missing this definition from libc/kernel headers unistd.h:

sandbox.c:184:40: error: '__NR_userfaultfd' undeclared (first use in
this function)

.gitlab-ci.yml

@@ -3,16 +3,6 @@ stages:
   - build_pkg
   - upload
 
-build:src:
-  stage: build_src
-  image: "ai/build:base"
-  script: "build-dsc"
-  artifacts:
-    paths:
-      - build-deb/
-  only:
-    - master
-
 build:src-stretch:
   stage: build_src
   image: "ai/build:stretch"
@@ -23,18 +13,6 @@ build:src-stretch:
   only:
     - master
 
-build:pkg:
-  stage: build_pkg
-  image: "ai/build:base"
-  script: "build-deb"
-  dependencies:
-    - build:src
-  artifacts:
-    paths:
-      - output-deb/
-  only:
-    - master
-
 build:pkg-stretch:
   stage: build_pkg
   image: "ai/build:stretch"
@@ -47,15 +25,6 @@ build:pkg-stretch:
   only:
     - master
 
-upload:jessie:
-  stage: upload
-  image: "ai/pkg:base"
-  script: "upload-packages"
-  dependencies:
-    - build:pkg
-  only:
-    - master
-
 upload:stretch:
   stage: upload
   image: "ai/pkg:base"