[next-rebased] scripts are not installed under /usr/share/wireplumber

When installing WirePlumber on the system using the next-rebased branch, scripts are installed under /usr/share/pipewire/scripts instead of /usr/share/wireplumber/scripts. We should have them installed under /usr/share/wireplumber/scripts like master, as they don't have anything to do with pipewire.

See #429 (closed)