Remove out-of-date kwant conda channel link

1 job for kwant-329 in 24 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
failed test_deploy #87319

00:00:24

 
Name Stage Failure
failed
test_deploy Test
Warning: Permanently added 'kwant-project.org,31.170.123.80' (ECDSA) to the list of known hosts.
Permission denied, please try again.
Permission denied, please try again.
Permission denied (publickey,password).
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: unexplained error (code 255) at io.c(226) [sender=3.1.1]
[2019-11-25T06:01:51Z] ERROR: deploy: Failed deployment -- command rsync -rlv -e 'ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -i deploy_key' --delete --filter 'P doc/*' --filter 'P extensions/*' output/* kwant@kwant-project.org: returned 255
Authenticating with credentials from /root/.docker/config.json
ERROR: Job failed: exit code 1