2.x: Fix excess item retention in the other replay components

[akarnokd]

This is a follow-up PR to #5892 in order to avoid item retention in the head node. For the ReplayProcessor, the cleanup can be triggered with cleanupBuffer. For the replay() operators, such trigger is not possible. However, the terminal events will perform the cleanup internally at least.

[codecov]

Codecov Report

Merging #5898 into 2.x will increase coverage by 0.04%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                2.x    #5898      +/-   ##
============================================
+ Coverage     97.92%   97.96%   +0.04%     
- Complexity     5984     5988       +4     
============================================
  Files           655      655              
  Lines         43863    43899      +36     
  Branches       6076     6082       +6     
============================================
+ Hits          42953    43007      +54     
+ Misses          281      274       -7     
+ Partials        629      618      -11

Impacted Files	Coverage Δ	Complexity Δ
...ex/internal/operators/flowable/FlowableReplay.java	92.79% <100%> (+0.1%)	22 <0> (ø)	⬇️
.../java/io/reactivex/processors/ReplayProcessor.java	99.38% <100%> (+0.02%)	52 <1> (+1)	⬆️
...nternal/operators/observable/ObservableReplay.java	98.63% <100%> (+0.02%)	23 <0> (ø)	⬇️
.../io/reactivex/internal/functions/ObjectHelper.java	94.73% <0%> (-5.27%)	20% <0%> (-1%)
...nternal/operators/parallel/ParallelReduceFull.java	91.08% <0%> (-3.97%)	2% <0%> (ø)
...tivex/internal/schedulers/TrampolineScheduler.java	96.1% <0%> (-2.6%)	6% <0%> (ø)
...java/io/reactivex/processors/PublishProcessor.java	98.23% <0%> (-1.77%)	43% <0%> (-1%)
...x/internal/operators/flowable/FlowablePublish.java	96.03% <0%> (-1.33%)	11% <0%> (ø)
...rnal/operators/flowable/FlowableSequenceEqual.java	97.56% <0%> (-1.22%)	2% <0%> (ø)
...ternal/operators/completable/CompletableMerge.java	96.42% <0%> (-1.2%)	2% <0%> (ø)
... and 21 more

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