sanitize tsk_is_polling()

Make default just return 0.  The current default (checking
TIF_POLLING_NRFLAG) is taken to architectures that need it;
ones that don't do polling in their idle threads don't need
to defined TIF_POLLING_NRFLAG at all.

ia64 defined both TS_POLLING (used by its tsk_is_polling())
and TIF_POLLING_NRFLAG (not used at all).  Killed the latter...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/c6x/include/asm/thread_info.h

@@ -97,7 +97,6 @@ struct thread_info *current_thread_info(void)
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
 
-#define TIF_POLLING_NRFLAG	16	/* true if polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17	/* OOM killer killed process */
 
 #define TIF_WORK_MASK		0x00007FFE /* work on irq/exception return */