atomic, cloud: remove rhgb by removing plymouth
a59dfe5 caused us a few problems:
- sed was breaking the symlink on atomic systems
- /boot/grub2/grub.cfg is not the right file on a UEFI system
- etc..
We'll solve this problem a different way by just not installing
plymouth in our systems, which is another way [1] to make sure
rhgb/quiet don't appear on your kernel command line.
[1] https://github.com/rhinstaller/anaconda/blob/ee91db6fa3972668b05808b3c7de125a7edd581f/pyanaconda/payload/__init__.py#L722-L726