.gitlab-ci.yml: retiring acadia

Acadia, we hardly knew you...

@sly2j Seems like a good time to stop worrying about having to keep material maps for acadia working... Let me know if you want to keep this alive.

.gitlab-ci.yml

@@ -335,7 +335,6 @@ jug_xl:feature:
     matrix:
       - DETECTOR: athena
         DETECTOR_BRANCH:
-          - acadia
           - canyonlands
           - deathvalley
           - deathvalley-1.5T