ARM: shmobile: sh73a0: Remove obsolete inclusion of <asm/smp_twd.h>

As of commit 9a986398 ("ARM: shmobile: Remove legacy SoC code
for SH-Mobile AG5"), this header file is no longer used.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>