DragonFlyBSD/src f29ea48. Makefile_upgrade.inc, include signal.h

kernel/libc: Remove sigstack() remains.

There is no sigstack() syscall anymore in DragonFly, besides being
obsolete, so remove some remains like the manual page and prototype,
and do some related cleanup.
DeltaFile
+0-51lib/libc/sys/sigstack.2
+0-10sys/sys/signal.h
+0-8sys/sys/sysproto.h
+0-3include/signal.h
+1-2sys/kern/syscalls.master
+1-1sys/kern/init_sysent.c
+1-1lib/libc/sys/Makefile.inc
+1-1lib/libc/sys/sigaltstack.2
+1-1sys/kern/syscalls.c
+1-1sys/sys/syscall.h
+1-0Makefile_upgrade.inc
+7-7911 files

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