Remove mistral legacy jobs
Remove mistral legacy jobs

These jobs have been migrated in-repo, remove them.

Change-Id: Ie558bc7f2741f53a5ba743c206452c7ccd2051d6
Needed-By: Ie2ec9d771843949ffa62da8b54fb7a3fc34c3241

openstack-infra/project-config,openstack-infra/project-config