ci: simplify CI configuration by removing unused variables

Removes unnecessary Docker variables and services from the CI 
configuration. This streamlines the build process and reduces 
complexity, improving overall maintenance and clarity.

.gitlab-ci.yml

@@ -8,15 +8,10 @@ include:
 stages:
 - build
 
-variables:
-  DOCKER_HOST: tcp://docker:2375/
-
 image: buildtool/build-tools:${BUILDTOOLS_VERSION}
 
 build:
   stage: build
-  services:
-  - docker:${DOCKER_DIND_VERSION}
   script:
   - build
   - curl -Os https://uploader.codecov.io/latest/linux/codecov