mm/Kconfig: remove default DISCONTIGMEM_MANUAL

Commit 214496cb ("ia64: make SPARSEMEM default and disable
DISCONTIGMEM") removed the last enabler of ARCH_DISCONTIGMEM_DEFAULT,
hence the memory model can no longer default to DISCONTIGMEM_MANUAL.

Link: https://lkml.kernel.org/r/20210312141208.3465520-1-geert@linux-m68k.orgSigned-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: NMike Rapoport <rppt@linux.ibm.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -9,7 +9,6 @@ config SELECT_MEMORY_MODEL
 choice
 	prompt "Memory model"
 	depends on SELECT_MEMORY_MODEL
-	default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
 	default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
 	default FLATMEM_MANUAL
 	help