Remove some functions that have the same effect as the bytes package

[bestgopher]

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There are two same functions in github.com/gin-gonic/gin/internal/bytesconv.

[codecov]

Codecov Report

Merging #2387 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2387      +/-   ##
==========================================
- Coverage   98.64%   98.63%   -0.01%     
==========================================
  Files          41       41              
  Lines        2359     2348      -11     
==========================================
- Hits         2327     2316      -11     
  Misses         18       18              
  Partials       14       14              

Impacted Files	Coverage Δ
tree.go	100.00% <100.00%> (ø)

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