2.x: FlowableTimeoutTimed - replace AtomicReference with mutable field

[davidmoten]

As per discussion in #5461. The timer fields in the Subscriber classes in FlowableTimeoutTimed are AtomicReferences but this is not required as the fields are accessed synchronously.

The timer field in TimeoutTimedOtherSubscriber did require an AtomicReference because of the dispose call here but this call is not required if we just call worker.dispose().

No unit test additions.

P.S. 9321 unit tests in RxJava 2.x! An outrageous amount of work, thanks @akarnokd (and other contributors)!

[codecov]

Codecov Report

Merging #5466 into 2.x will decrease coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                2.x    #5466      +/-   ##
============================================
- Coverage     95.94%   95.91%   -0.04%     
- Complexity     5797     5801       +4     
============================================
  Files           631      631              
  Lines         41306    41297       -9     
  Branches       5745     5743       -2     
============================================
- Hits          39633    39610      -23     
- Misses          656      669      +13     
- Partials       1017     1018       +1

Impacted Files	Coverage Δ	Complexity Δ
...ernal/operators/flowable/FlowableTimeoutTimed.java	93.22% <100%> (+1.09%)	4 <0> (ø)	⬇️
...nternal/operators/observable/ObservableCreate.java	92.3% <0%> (-5.99%)	2% <0%> (ø)
...vex/internal/operators/single/SingleTakeUntil.java	86.88% <0%> (-4.92%)	2% <0%> (ø)
...rnal/subscriptions/DeferredScalarSubscription.java	93.84% <0%> (-4.62%)	27% <0%> (-1%)
...ternal/operators/flowable/FlowableSampleTimed.java	91.17% <0%> (-4.42%)	3% <0%> (ø)
...ernal/operators/maybe/MaybeTakeUntilPublisher.java	96% <0%> (-4%)	2% <0%> (ø)
...internal/disposables/ArrayCompositeDisposable.java	96.42% <0%> (-3.58%)	15% <0%> (-1%)
...ex/internal/subscriptions/SubscriptionArbiter.java	95.76% <0%> (-3.39%)	45% <0%> (-2%)
...rnal/operators/flowable/FlowableFlatMapSingle.java	91.3% <0%> (-3.27%)	2% <0%> (ø)
...in/java/io/reactivex/subjects/BehaviorSubject.java	82.81% <0%> (-3.13%)	56% <0%> (-1%)
... and 42 more

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