[cleanup] [broker] fix doc for TransactionBuffer#isTxnAborted

[thetumbled]

Motivation

The argument PositionImpl readPosition of method org.apache.pulsar.broker.transaction.buffer.TransactionBuffer#isTxnAborted is weird and unneccessary, we have better remove it to avoid confusion.
Argument PositionImpl readPosition is used for future.

Modifications

Remove the argument PositionImpl readPosition.
fix the doc and add to-do to avoid confusion.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: thetumbled#36

[thetumbled]

PTAL, thanks. @congbobo184 @liangyepianzhou

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b14fcb4) 73.60% compared to head (55e0ea0) 73.62%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #21956      +/-   ##
============================================
+ Coverage     73.60%   73.62%   +0.01%     
- Complexity    32411    32441      +30     
============================================
  Files          1861     1861              
  Lines        138674   138676       +2     
  Branches      15182    15184       +2     
============================================
+ Hits         102070   102096      +26     
+ Misses        28702    28696       -6     
+ Partials       7902     7884      -18     

Flag	Coverage Δ
inttests	24.08% <ø> (-0.12%)	⬇️
systests	23.63% <ø> (-0.09%)	⬇️
unittests	72.92% <ø> (+0.03%)	⬆️

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see 73 files with indirect coverage changes