Remove obsolete JFrog references in README.md

[izeye]

This PR removes the obsolete JFrog references in the README.md.

[codecov]

Codecov Report

Merging #7519 (951c4ce) into 3.x (baad331) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                3.x    #7519      +/-   ##
============================================
- Coverage     99.59%   99.56%   -0.04%     
+ Complexity     6799     6797       -2     
============================================
  Files           752      752              
  Lines         47670    47670              
  Branches       6399     6399              
============================================
- Hits          47477    47461      -16     
- Misses           88       94       +6     
- Partials        105      115      +10     

Impacted Files	Coverage Δ
.../operators/flowable/FlowableBlockingSubscribe.java	93.02% <0.00%> (-4.66%)	⬇️
...nternal/operators/parallel/ParallelReduceFull.java	91.08% <0.00%> (-3.97%)	⬇️
...ternal/operators/completable/CompletableMerge.java	97.29% <0.00%> (-2.71%)	⬇️
.../operators/observable/ObservableFlatMapSingle.java	94.44% <0.00%> (-2.39%)	⬇️
...o/reactivex/rxjava3/processors/AsyncProcessor.java	97.91% <0.00%> (-2.09%)	⬇️
...ernal/operators/flowable/FlowableFlatMapMaybe.java	96.89% <0.00%> (-1.56%)	⬇️
...rnal/operators/flowable/FlowableFlatMapSingle.java	94.18% <0.00%> (-1.17%)	⬇️
...ternal/operators/observable/ObservableFlatMap.java	97.87% <0.00%> (-1.07%)	⬇️
...3/internal/operators/flowable/FlowablePublish.java	99.00% <0.00%> (-1.00%)	⬇️
...a/io/reactivex/rxjava3/subjects/ReplaySubject.java	99.16% <0.00%> (-0.42%)	⬇️
... and 2 more

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