[CP-stable][win32] Remove the predicate from TimerThread condition variable - #193238

…tter#193181)

Right now we're not checking the next_fire_time_ in the predicate, which
means that when scheduling an earlier timer, we signal the condition
variable but because of the missing check it is ignored as spurious
wake-up.

This is the second time we got the predicate wrong. The loop can handle
spurious wake-ups just fine, so it's probably best to remove the
predicate.

This might account for some of the win32 tests flakiness.

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