enhance: Remove not inuse binlog iterators

[XuanYang-cn]

1. Remove datanode/iterators/binlog_iterator
2. Remove storage/binlog_iterator/MergeIterator

See also: #39242

[sre-ci-robot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.03%. Comparing base (7addeea) to head (d510ea6).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #39243      +/-   ##
==========================================
- Coverage   81.08%   81.03%   -0.05%     
==========================================
  Files        1405     1404       -1     
  Lines      198290   198183     -107     
==========================================
- Hits       160790   160605     -185     
- Misses      31858    31915      +57     
- Partials     5642     5663      +21     

Components	Coverage Δ
Client	79.50% <ø> (ø)
Core	69.65% <ø> (ø)
Go	82.95% <ø> (-0.06%)	⬇️

Files with missing lines	Coverage Δ
internal/storage/binlog_iterator.go	93.33% <ø> (-0.61%)	⬇️

... and 31 files with indirect coverage changes

[mergify]

@XuanYang-cn go-sdk check failed, comment rerun go-sdk can trigger the job again.