remove did and move to bind-mounting docker socket

This allows IPv6 in the build container which is a requirement.

.gitlab-ci.yml

 image: docker:latest
 
-services:
-  - name: docker:dind
-    # MTU 1400 for hetzner vSwitch
-    command: ["--mtu=1400"]
-
 stages:
 - build
 
 variables:
   IMAGE_TAG: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
-  DOCKER_HOST: tcp://docker:2375
   DOCKER_TLS_CERTDIR: ""
 
 cache: