RFC: Don't generate appstream data for packages

The kpackage_install_package function generates appstream data from the package metadata.

While a nice concept in general it poses some practical problems.

Since lots of first-party Plasma content like applets is shipped via KPackage it makes those components show up in software centers like discover. This makes them appear as independently (un)installable things, which they are not, because from the package manager's POV they are part of a larger package like plasma-workspace. Attempting to uninstall them will in the best case outright fail and in the worst case horribly break the system.

It's also something that frequently confuses users.

To avoid this drop the automatic appstream generation