ci-update-from-upstream: Drop now-unused separate pipeline
With the switch to the external CI config across all the packaging
projects we have necessarily switched to the single pipeline definition
from commit cf2a80ff, which merged ci-update-from-upstream.yml
into ci-package-builder.yml
.
Nowe that we have dropped all the debian/*-gitlab-update-job
branches
which still held a reference to ci-update-from-upstream.yml
we can
finally drop it.