gitlab-ci: No need for our ci repository

Just using debian buster makes things more stable.

.gitlab-ci.yml

@@ -4,10 +4,6 @@ stages:
   - build
 
 before_script:
-  - apt-get -y update
-  - apt-get -y install wget gnupg2
-  - echo "deb http://ci.puri.sm/ scratch librem5" > /etc/apt/sources.list.d/ci.list
-  - wget -O- https://ci.puri.sm/ci-repo.key | apt-key add -
   - apt-get -y update
   - apt-get -y build-dep .