For normal distros it doesn't make sense, KDE_INSTALL_FULL_DATAROOTDIR
will be /usr/.
For devs using a prefix startplasma-dev.sh already does this for us only
for the dev setup.
For any other user, it should be their responsibility to adjust it.
It's currently broken anyway, if a user simply installs flatpak that sets this env
earlier in the boot, so this will do nothing. It implies no-oe relies on thisl
It's a relic from 2007 (bd38d59e11548f160efd0918ca5461536ac72349) that doesn't
make sense now.