Change I55abe50b4206e803b7a42f3f162334009c908a99 removed the playbooks
for legacy-puppet-beaker-rspec-centos-7 wrongly. Looking deeper, those
jobs are for puppet 3 which is EOL for some time. Remove only user which
is in puppet-midonet and puppet-midonet has no merges since 2017.
Similar for legacy-puppet-beaker-rspec, this is unused now.
Remove other puppet 3 jobs as well.
Depends-On: https://review.opendev.org/659912
Change-Id: I04cd3d60fc4d4ac2f36afe388dd61c173e9ad966