This reverts commit 7f058d61a10384ca81c88245c4ff80c08f89ad6b.
Reverting because of bug 2284 [1] where grub will sometimes fail due to
memory corruption. This is _not_ the cause of the bug, and the bug can
even be reproduced with this reversion, but it seems to occur less when
not using fat32.
[1] https://github.com/coreos/bugs/issues/2284