[PATCH] mm: fix swap unused warning

If CONFIG_SWAP is not defined we get:

mm/vmscan.c: In function â\80\98remove_mappingâ\80\99:
mm/vmscan.c:387: warning: unused variable â\80\98swapâ\80\99

Convert defines in swap.h into blank inline functions to fix this warning
and be consistent.

Signed-off-by: Con Kolivas <kernel@kolivas.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>