This is done now. We stopped using gitblit for good!:)
git.wikimedia.org URLs now redirect to Diffusion.
redirect rules here: https://gerrit.wikimedia.org/r/#/c/296138/
tested URLs here: https://phabricator.wikimedia.org/P3318
https://phabricator.wikimedia.org/T137224 was resolved
https://phabricator.wikimedia.org/T111465 can be closed
antimony was removed from varnish config: https://gerrit.wikimedia.org/r/#/c/293789/
one more precise host can be shut down ...
thanks to Paladox, Danny_B and JanZerebecki