[Cherry-Pick] Remove unused iterator initialization

[congqixia]

Cherry-pick from master /kind improvement

[sre-ci-robot]

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[jiaoew1991]

/lgtm

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[codecov[bot]]

Codecov Report

Merging #24758 (39240a5) into 2.2.0 (a03ebcf) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff           @@
##            2.2.0   #24758   +/-   ##
=======================================
  Coverage   80.67%   80.68%           
=======================================
  Files         760      760           
  Lines      106999   106998    -1     
=======================================
+ Hits        86320    86329    +9     
+ Misses      17357    17355    -2     
+ Partials     3322     3314    -8     

Impacted Files	Coverage Δ
internal/kv/rocksdb/rocks_iterator.go	72.09% <ø> (ø)
internal/kv/rocksdb/rocksdb_kv.go	83.92% <ø> (-0.06%)	:arrow_down:

... and 23 files with indirect coverage changes

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[jiaoew1991]

/lgtm