3.x: Remove now unnecessary unchecked warning suppressions

[akarnokd]

Most varargs places now have @SafeVarargs so there is no need for @SuppressWarnings("unchecked"). Some non-test classes need still updating though.

[codecov]

Codecov Report

Merging #6790 into 3.x will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##               3.x    #6790      +/-   ##
===========================================
+ Coverage     98.2%   98.23%   +0.03%     
- Complexity    6283     6286       +3     
===========================================
  Files          696      696              
  Lines        45390    45390              
  Branches      6233     6233              
===========================================
+ Hits         44574    44590      +16     
+ Misses         288      280       -8     
+ Partials       528      520       -8

Impacted Files	Coverage Δ	Complexity Δ
.../operators/flowable/FlowableBlockingSubscribe.java	93.02% <0%> (-4.66%)	10% <0%> (-1%)
...eactivex/rxjava3/processors/BehaviorProcessor.java	96.58% <0%> (-1.47%)	51% <0%> (+1%)
...ternal/operators/completable/CompletableMerge.java	95.94% <0%> (-1.36%)	2% <0%> (ø)
...operators/observable/ObservableMergeWithMaybe.java	99.09% <0%> (-0.91%)	2% <0%> (ø)
...a3/internal/operators/flowable/FlowableReplay.java	91.97% <0%> (-0.83%)	19% <0%> (ø)
...al/operators/observable/ObservableWindowTimed.java	96.12% <0%> (-0.65%)	4% <0%> (ø)
...rnal/operators/observable/ObservableSwitchMap.java	91.57% <0%> (-0.53%)	3% <0%> (ø)
...va3/internal/operators/parallel/ParallelRunOn.java	96.61% <0%> (-0.49%)	8% <0%> (ø)
.../reactivex/rxjava3/processors/ReplayProcessor.java	97.34% <0%> (-0.41%)	52% <0%> (ø)
...a/io/reactivex/rxjava3/subjects/ReplaySubject.java	97.51% <0%> (+0.41%)	50% <0%> (ø)	⬇️
... and 8 more

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