um: -include user.h for USER_OBJ, trim includes

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/sigio.c

@@ -11,14 +11,12 @@
 #include <sched.h>
 #include <signal.h>
 #include <string.h>
-#include "kern_constants.h"
 #include "kern_util.h"
 #include "init.h"
 #include "os.h"
 #include "process.h"
 #include "sigio.h"
 #include "um_malloc.h"
-#include "user.h"
 
 /*
  * Protected by sigio_lock(), also used by sigio_cleanup, which is an