workqueue: remove unused work_clear_pending()

In 8930caba3dbd ("workqueue: disable irq while manipulating PENDING"),
setting last CPU and clearing PENDING got merged into a single
operation (set_work_cpu_and_clear_pending()), which resulted that the
internal routine work_clear_pending() is not used any more.

tj: Minor description tweak.

Signed-off-by: Lai Jiangshan <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

include/linux/workqueue.h

···
 #define delayed_work_pending(w) \
 	work_pending(&(w)->work)
 
-/**
- * work_clear_pending - for internal use only, mark a work item as not pending
- * @work: The work item in question
- */
-#define work_clear_pending(work) \
-	clear_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))
-
 /*
  * Workqueue flags and constants.  For details, please refer to
  * Documentation/workqueue.txt.