Removes Support For TransformChatHistory and CompressibleAgent

[WaelKarkoub]

Why are these changes needed?

Doing some cleanup, removing TransformChatHistory and CompressibleAgent in favor of TransformMessages.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 21.98%. Comparing base (6279247) to head (246015e).
Report is 80 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3313       +/-   ##
===========================================
- Coverage   32.90%   21.98%   -10.92%     
===========================================
  Files          94       95        +1     
  Lines       10235    10637      +402     
  Branches     2193     2442      +249     
===========================================
- Hits         3368     2339     -1029     
- Misses       6580     8128     +1548     
+ Partials      287      170      -117     

Flag	Coverage Δ
unittests	21.94% <ø> (-10.97%)	⬇️

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[marklysze]

Thanks @WaelKarkoub, should we remove this section from the FAQ?

Rest looks good to me :)