2.x: Use different wording on blockingForEach() JavaDocs

[akarnokd]

Change the wording on the blockingForEach() method to clarify it runs the Consumer on the current thread. Since there is no onError callback, the extra sentence about the error behavior was removed. There is an error handling section already that explains it properly.

[codecov]

Codecov Report

Merging #6057 into 2.x will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #6057      +/-   ##
============================================
- Coverage     98.29%   98.26%   -0.04%     
+ Complexity     6193     6192       -1     
============================================
  Files           666      666              
  Lines         44802    44802              
  Branches       6206     6206              
============================================
- Hits          44039    44024      -15     
- Misses          229      238       +9     
- Partials        534      540       +6

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Observable.java	100% <ø> (ø)	539 <0> (ø)	⬇️
src/main/java/io/reactivex/Flowable.java	100% <ø> (ø)	564 <0> (ø)	⬇️
...l/operators/observable/ObservableFlatMapMaybe.java	87.58% <0%> (-9.16%)	2% <0%> (ø)
...tivex/internal/observers/FutureSingleObserver.java	94.33% <0%> (-3.78%)	24% <0%> (-1%)
...reactivex/internal/operators/single/SingleAmb.java	96.36% <0%> (-3.64%)	9% <0%> (-1%)
...ava/io/reactivex/processors/BehaviorProcessor.java	96.86% <0%> (-2.25%)	60% <0%> (ø)
...x/internal/operators/flowable/FlowablePublish.java	97.02% <0%> (-2.13%)	11% <0%> (ø)
.../operators/observable/ObservableFlatMapSingle.java	88.8% <0%> (-1.5%)	2% <0%> (ø)
...nternal/operators/observable/ObservableCreate.java	94.87% <0%> (-0.86%)	2% <0%> (ø)
...perators/single/SingleFlatMapIterableFlowable.java	97.5% <0%> (-0.84%)	2% <0%> (ø)
... and 16 more

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