powerpc/boot: Remove bogus reference to lilo

The help text refers to lilo, but the install script does not run lilo
and never has. The reference to lilo seems to have come originally from
arch/ppc/Makefile, but it was not true there either.

Remove it.

Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
Link: https://fosstodon.org/@kernellogger/113032940928131612


Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241009053806.135807-1-mpe@ellerman.id.au