ARM: remove unused arch_decomp_wdog()

With ARCH_HAS_DECOMP_WDOG removed from arch/arm/boot/compressed/decompress.c,
all the arch_decomp_wdog() definition at platform level is unneeded.
Remmove it.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Jason Cooper <jason@lakedaemon.net>

arch/arm/mach-rpc/include/mach/uncompress.h

@@ -189,8 +189,3 @@ static void arch_decomp_setup(void)
 	if (nr_pages * page_size < 4096*1024) error("<4M of mem\n");
 }
 #endif
-
-/*
- * nothing to do
- */
-#define arch_decomp_wdog()