gitlab: Skip the docker-in-docker step

No idea which cult's cargo I was looking at there. Cuts about a minute
off the build time.

Signed-off-by: Adam Jackson <ajax@redhat.com>

.gitlab-ci.yml

@@ -1,13 +1,5 @@
-image: docker:latest
-services:
-    - docker:dind
-
-before_script:
-    - echo FROM nwnk/xserver-travis-rawhide:v5 > Dockerfile
-    - echo ADD . /root >> Dockerfile
-    - echo WORKDIR /root >> Dockerfile
-    - docker build -t withgit .
+image: nwnk/xserver-travis-rawhide:v5
 
 job:
     script:
-        - docker run --volume $HOME/.ccache:/root/.ccache withgit ./test/scripts/build-travis-deps.sh
+        - ./test/scripts/build-travis-deps.sh