The vmlinuz kernel image gets installed to /usr/boot/ but isn't usable
for dm-verity until it gets copied over to /boot/flatcar/ and the hash
gets embedded at a particular offset. The file in /usr/boot/ uses space
while it's not having a real purpose as long as dm-verity is used.
Delete the vmlinuz file under /usr/boot/ to free up space. When
generating the ISO image we use the vmlinuz file from /boot/flatcar/
which also has the advantage that we only distribute a single vmlinuz
file with one particular checksum.
c1b2d88aa2