ui/input-barrier: Move TODOs from barrier.txt to a comment

docs/barrier.txt has a couple of TODO notes about things to be
implemented in this device; move them into a comment in the
source code.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210727204112.12579-3-peter.maydell@linaro.org

docs/barrier.txt

@@ -45,8 +45,4 @@
 
         (qemu) object_del barrier0
         (qemu) object_add input-barrier,id=barrier0,name=VM-1
-* TO DO
-
-    - Enable SSL
-    - Manage SetOptions/ResetOptions commands
 

ui/input-barrier.c

@@ -3,6 +3,11 @@
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
+ *
+ * TODO:
+ *
+ *  - Enable SSL
+ *  - Manage SetOptions/ResetOptions commands
  */
 
 #include "qemu/osdep.h"