Remove references to the deprecated "make prepare-all" target from the
top-level Makefile; use just "make prepare" instead.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Oleg Verych <olecom@flower.upol.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>