timers: fix performance regression
timers: fix performance regression

Fix a 5-7% performance regression in the http_simple benchmark that was
introduced by the following commits:

  348d8cd timers: remove _idleTimeout from item in .unenroll()
  f2f3028 timers: fix memory leak in setTimeout
  098fef6 timers: remember extra setTimeout() arguments when timeout==0

Fix suggested by Bert Belder.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node