2.x: Remove commented out code in IoScheduler

[Mauin]

Removes some code that was commented out in IoScheduler. Those lines were last edited in 2 years ago, so I assume they should be safe to delete.

[codecov]

Codecov Report

Merging #5268 into 2.x will increase coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #5268      +/-   ##
============================================
+ Coverage     96.01%   96.06%   +0.05%     
- Complexity     5746     5753       +7     
============================================
  Files           628      628              
  Lines         41077    41077              
  Branches       5699     5699              
============================================
+ Hits          39440    39462      +22     
+ Misses          651      637      -14     
+ Partials        986      978       -8

Impacted Files	Coverage Δ	Complexity Δ
.../io/reactivex/internal/schedulers/IoScheduler.java	92.39% <ø> (-1.09%)	9 <0> (ø)
.../operators/completable/CompletableConcatArray.java	93.75% <0%> (-6.25%)	2% <0%> (ø)
.../internal/operators/maybe/MaybeTakeUntilMaybe.java	93.87% <0%> (-4.09%)	2% <0%> (ø)
...vex/internal/operators/flowable/FlowableTimer.java	92.85% <0%> (-3.58%)	2% <0%> (ø)
.../operators/observable/ObservableFlatMapSingle.java	93.28% <0%> (-2.24%)	2% <0%> (ø)
...rnal/operators/observable/ObservableObserveOn.java	97.95% <0%> (-2.05%)	3% <0%> (ø)
...perators/single/SingleFlatMapIterableFlowable.java	96.66% <0%> (-1.67%)	2% <0%> (ø)
...vex/internal/operators/single/SingleTakeUntil.java	86.88% <0%> (-1.64%)	2% <0%> (ø)
...vex/internal/operators/parallel/ParallelRunOn.java	94.41% <0%> (-1.53%)	6% <0%> (ø)
...ternal/operators/flowable/FlowableSampleTimed.java	95.58% <0%> (-1.48%)	3% <0%> (ø)
... and 36 more

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