Remove docs-on-readthedocs-failing
Remove docs-on-readthedocs-failing

Now that Armada has correctly followed the new docs-on-readthedocs
pattern here [0] we can drop this job from project-config.

[0] https://review.openstack.org/#/c/601297/

Change-Id: I8f971a2486c28d85c253063675c6edaccb881d32

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