sh: remove meaningless archclean line

The vsyscall directory is cleaned up by the ordinary way
via arch/sh/kernel/Makefile:

  obj-$(CONFIG_VSYSCALL)          += vsyscall/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

arch/sh/Makefile

@@ -200,7 +200,6 @@ archprepare:
 
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)
-	$(Q)$(MAKE) $(clean)=arch/sh/kernel/vsyscall
 
 archheaders:
 	$(Q)$(MAKE) $(build)=arch/sh/kernel/syscalls all