Description of problem:
As decided, kubevirt platform is defined as "dev preview", therefore kubevirt-machine-controllers image is not included in release
Remove this image from machine-api to prevent failures during the missing image
Note on the lack of a 4.8 blocking bug: the image will ship with 4.8, so we want to remove it in 4.7 while leaving it in in 4.8. Leaving the image in 4.8 is the goal, not a regression ;).