um: Remove SKAS3/4 support

Before we had SKAS0 UML had two modes of operation
TT (tracing thread) and SKAS3/4 (separated kernel address space).
TT was known to be insecure and got removed a long time ago.
SKAS3/4 required a few (3 or 4) patches on the host side which never went
mainline. The last host patch is 10 years old.

With SKAS0 mode (separated kernel address space using 0 host patches),
default since 2005, SKAS3/4 is obsolete and can be removed.

Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/process.c

@@ -16,7 +16,6 @@
 #include <init.h>
 #include <longjmp.h>
 #include <os.h>
-#include <skas_ptrace.h>
 
 #define ARBITRARY_ADDR -1
 #define FAILURE_PID    -1
@@ -102,21 +101,6 @@ void os_kill_process(int pid, int reap_child)
 		CATCH_EINTR(waitpid(pid, NULL, __WALL));
 }
 
-/* This is here uniquely to have access to the userspace errno, i.e. the one
- * used by ptrace in case of error.
- */
-
-long os_ptrace_ldt(long pid, long addr, long data)
-{
-	int ret;
-
-	ret = ptrace(PTRACE_LDT, pid, addr, data);
-
-	if (ret < 0)
-		return -errno;
-	return ret;
-}
-
 /* Kill off a ptraced child by all means available.  kill it normally first,
  * then PTRACE_KILL it, then PTRACE_CONT it in case it's in a run state from
  * which it can't exit directly.