qemu-iotests: Simplify 109 with unaligned qemu-img compare

For some time now, qemu-img compare has been able to compare
unaligned images.  So we no longer need test 109's hack of
resizing to sector boundaries before invoking compare.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 1463416983-28318-3-git-send-email-eblake@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
