As melodic is the default and should be used on all recent platforms.
The old version of packages are kept only for xenial, not the other way.

Affected packages:

- wip/pal-gazebo-plugins-melodic
- wip/pal-gazebo-worlds
- wip/pal-hardware-gazebo-melodic
- wip/prf-gazebo-ros-pkgs-melodic
- wip/prf-roboticsgroup-gazebo-plugins
- wip/talos-dev
- wip/talos-simulation
- wip/tiago-description-calibration
- wip/tiago-dev
- wip/tiago-simulation
- wip/tiago-tutorials