Bug#1033524: Simplify the instructions for making bootable media

[Chris Hofstaedtler]

* Steve McIntyre <st...@einval.com>:
> We should definitely also kill section 4.4.2: Loadlin is *dead* -
> *nobody* has DOS any more.

Section 5.1.4. "Booting from DOS using loadlin" should also go, I
guess.