net: remove redundant check for timer pending state before del_timer

As in del_timer() there has already placed a timer_pending() function
to check whether the timer to be deleted is pending or not, it's
unnecessary to check timer pending state again before del_timer() is
called.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>