jobs: remove artifacts-days/num-to-keep: -1

Remove the "artifact-days-to-keep: -1" and "artifact-num-to-keep: -1"
lines, as they don't have an effect. -1 is the default value, which
means "infinite" and causes the value from "days-to-keep" /
"num-to-keep" to get used instead.

This patch re-applies part of 719ff976 ("jobs: tweak build-discarder
values"), which had been reverted in a052c13c.

Related: https://jenkins-job-builder.readthedocs.io/en/latest/properties.html#properties.build-discarder
Related: OS#5980
Change-Id: Ic073643634e1814147d765dd7e8f3f02e81effc3
11 files changed