Ports: Do not allow clean* to be overridden

There were only two packages making use of this functionality, but it
seems more sensible to have a fixed implementation for the cleaning of
ports - especially now they delete the entire build directory and/or
dist files.

Ports/qt6-qtbase/package.sh

@@ -57,7 +57,3 @@ install() {
     echo "The development of the Qt Serenity platform plugin is happening here. Fixes for things like input handling, window management and theme integration should go here:"
     echo -e "\t" "https://github.com/SerenityPorts/QSerenityPlatform"
 }
-
-clean() {
-    run ninja clean
-}