fedup is deprecated and abandoned. Let's save time and disk by not
building `upgrade.img` when nothing is going to use it anymore.
For the record, performing upgrades using an initramfs from the new
system turns out to be fragile and hard to support:
* dracut initramfs isn't generic enough to handle booting all systems
(e.g. missing vconsole.conf means you get keymaps wrong, so users
can't unlock encrypted disks)
* The ABI differences between the two versions of plymouth, systemd,
etc. requires nasty workarounds at best and causes nightmarish
systemd crashes at worst
This patch removes all the code that built and installed `upgrade.img`.
For backwards compatibility, the API retains the `doupgrade` keyword
argument, and the `--noupgrade` flag is still accepted.
