Remove spurious lightdm configuration. Refs: #968

1 job for master in 14 seconds (queued for 2 seconds)
Name Stage Failure
failed
build-buster Test
  on r2.medea.fuss.bz.it gymymFU_
Using Docker executor with image registry.gitlab.com/fusslab/builder:buster ...
Pulling docker image registry.gitlab.com/fusslab/builder:buster ...
Using docker image sha256:6d6624d837dd8423b4b546387d2e51649201b81570f7b139915f3083f0aef6aa for registry.gitlab.com/fusslab/builder:buster ...
Running on runner-gymymFU_-project-46-concurrent-0 via 4b1ae8056050...
Fetching changes with git depth set to 50...
Reinitialized existing Git repository in /builds/fuss/fuss-client/.git/
fatal: unable to access 'https://gitlab-ci-token:[MASKED]@gitlab.fuss.bz.it/fuss/fuss-client.git/': Could not resolve host: gitlab.fuss.bz.it
ERROR: Job failed: exit code 1