Re-enable prop_timeouts_io test

The `prop_timeouts_io withTimeoutSerialNative` is failing too often, and hence
was disabled. We should find a proper way of fixing this.

```
prop_timeouts_io withTimeoutSerialNative: FAIL (131.41s)
*** Failed! Falsified (after 53 tests):
[(0.01s,0.004s),(0.002s,0.003s),(0.002s,0.009s),(0.003s,0.01s),(0.005s,0s),(0.001s,0.003s),(0.01s,0.003s),(0.004s,0.01s),(0.001s,0.003s),(0.002s,0.005s),(0.004s,0.002s),(0.002s,0.001s),(0.002s,0.005s),(0.009s,0.002s),(0.002s,0.005s),(0.004s,0s),(0.01s,0.005s),(0s,0.003s),(0.001s,0.004s),(0.007s,0s),(0.004s,0.008s),(0.004s,0.004s),(0.002s,0.001s),(0.005s,0.005s),(0.009s,0.003s),(0.004s,0.01s),(0.005s,0.005s),(0.005s,0.004s),(0.005s,0.004s),(0s,0.002s),(0.003s,0.005s),(0s,0.008s),(0.004s,0.001s),(0.005s,0.007s),(0.005s,0.002s),(0s,0s),(0.002s,0s),(0s,0s),(0.004s,0.003s),(0.005s,0.005s),(0.008s,0.003s),(0.001s,0s),(0.004s,0.004s),(0.003s,0.005s),(0.009s,0.003s)]
failure on timeout test #8
intendedTimeoutDuration: 0.004s
intendedActionDuration: 0.01s
intendedOverallDuration: 0.004s
actualOverallDuration: 0.129451s
positiveSchedulingTolerance: 0.1s
violation of timer sanity property:
actualOverallDuration <= intendedOverallDuration
+ positiveSchedulingTolerance
Use --quickcheck-replay=342479 to reproduce.
```