Update README to reflect recent changes and removals

[akarnokd]

Another try as the entropy comment didn't show on the PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.68%. Comparing base (5dcdacb) to head (6c7db23).
⚠️ Report is 3 commits behind head on 4.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8265      +/-   ##
============================================
+ Coverage     98.61%   98.68%   +0.07%     
- Complexity     7147     7151       +4     
============================================
  Files           824      824              
  Lines         50768    50798      +30     
  Branches       6905     6909       +4     
============================================
+ Hits          50063    50131      +68     
+ Misses          482      467      -15     
+ Partials        223      200      -23     

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[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.708 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

.github/workflows/entropy-beauty-comment.yml: 4.506
README.md: 4.990
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromIterable.java: 4.438
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromStream.java: 4.850
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromStreamTest.java: 4.759

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊