genmsg: updating to 0.4.22

The genmsg recipe is updated to 0.4.22 to be in line with
https://github.com/ros/rosdistro/blob/4551e7c32d1b34984410b79bc0ec36afe3d3d245/hydro/release.yaml.
The previously applied patch has been included in 0.4.22 and is
removed from the recipe and this repository.
The PR variable is reset.