chore(ci): remove unused docker variables from configuration

This commit removes the redundant Docker-related variables from the
`.gitlab-ci.yml` file to simplify the CI configuration. The removed
variables are not utilized in the current build process and their
absence improves clarity and maintainability of the CI setup.

.gitlab-ci.yml

@@ -5,13 +5,6 @@ stages:
   - build
   - deploy
 
-variables:
-  DOCKER_HOST: tcp://docker:2376
-  DOCKER_TLS_CERTDIR: "/certs"
-  DOCKER_TLS_VERIFY: 1
-  DOCKER_CERT_PATH: "$DOCKER_TLS_CERTDIR/client"
-  DOCKER_DRIVER: overlay2
-
 image: buildtool/build-tools:${BUILDTOOLS_VERSION}
 
 build: