[PATCH] mm/Kconfig: kill unused ARCH_FLATMEM_DISABLE

This used to be used to disable FLATMEM selection, but I decided to change it
to be done generically when DISCONTIG is enabled.  The option is unused, so
this kills it.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>