ci: loading dune-env:2.5.1 image now. removed python3 build because image only contains python3

.gitlab-ci.yml

-image: dorie/dune-env:2.5
+image: dorie/dune-env:2.5.1
 
 variables:
   DUNE_CONTROL_PATH: /opt/dune:$CI_PROJECT_DIR
@@ -25,18 +25,6 @@ build:main:
       - $CI_PROJECT_DIR/build-cmake/doc/html/
     expire_in: 1 week
 
-build:python3:
-  tags:
-    - docker
-  script:
-    - ./dune-common/bin/dunecontrol --only=dune-python exec "rm -rf build-cmake"
-    - ./dune-common/bin/dunecontrol --only=dune-testtools exec "rm -rf build-cmake"
-    - ./dune-common/bin/dunecontrol --only=dorie exec "rm -rf build-cmake"
-    - CMAKE_FLAGS="-DDUNE_FORCE_PYTHON3=True" MAKE_FLAGS="-j 2" ./dune-common/bin/dunecontrol --module=dorie all
-    - export PATH=/opt/dune/dorie/build-cmake/bin:$PATH
-    - ARGS="--output-on-failure -j 2" ./dune-common/bin/dunecontrol --only=dorie make test
-  stage: build
-
 build:update_dune:
   tags:
     - docker