m68k: Drop remainings and API of BOOTINFO_COMPAT_1_0

Drop remainings and API for backwards compatibility with bootinfo interface
version 1.0.  This was used when booting a 2.1.x or newer kernel on Amiga,
Atari, or Mac using a bootstrap for kernel 2.0.x.

Everybody upgraded his bootstrap a long time ago, so this can go.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>