kernel/signal.c: remove some duplicated includes

tty.h and fs.h are included twice.  It's unnecessary.  so remove them.

Link: http://lkml.kernel.org/r/20181126150900.32235-1-tiny.windzz@gmail.comSigned-off-by: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

kernel/signal.c

@@ -19,8 +19,6 @@
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/sched/cputime.h>
-#include <linux/fs.h>
-#include <linux/tty.h>
 #include <linux/binfmts.h>
 #include <linux/coredump.h>
 #include <linux/security.h>