Replace `qtmpris` with `amber-mpris`.

[MagneFire]

We use a very old version of qtmpris: https://github.com/nemomobile/qtmpris/tree/62c55e43dad6a479439ada609741ebebc4adaf23 (2016).
Meanwhile the project has been migrated to the SailfishOS organization: https://github.com/sailfishos/qtmpris
But it seems to be refactored into amber-mpris here: https://github.com/sailfishos/amber-mpris.
And this is the refactor commit: sailfishos/amber-mpris@41f58a2

We should probably consider updating our packages to reflect this change as well. The additional benefit is that qtdbusextended (https://github.com/AsteroidOS/meta-asteroid/blob/master/recipes-nemomobile/qtdbusextended/qtdbusextended_git.bb) has been merged into qtmpris so we can remove that recipe entirely.