Revert "Disable the building of the KNS backend until it can be corrected to...

Revert "Disable the building of the KNS backend until it can be corrected to not cause a Denial of Service attack on KDE.org infrastructure."

This reverts commit f66df353.
It's not fixing anything and it only makes it harder to address whatever
problem we might have.


(cherry picked from commit fe931b9c)