sh: Rip out left-over nommu cond syscall cruft.

At some point way back when (2.5 or so) quite a few syscalls hadn't
yet been wired up as cond_syscalls(), so we opted to just do direct
sys_ni_syscall wrapping in the assembly code instead. That's all
been fixed up since then, so we can drop the wrapping.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>