chore: Delete duplicate variables

[yoyo837]

🤔 This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

💡 Background and solution

ref: #17273、 #17613

📝 Changelog

Language	Changelog
🇺🇸 English
🇨🇳 Chinese	删除重复的@menu-icon-size 、@menu-icon-size-lg、@menu-dark-selected-item-icon-color、@menu-dark-selected-item-text-color; 调整顺序；删除@dark-menu-item-hover-bg，这里应该是笔误，另有@menu-dark-item-hover-bg ；

☑️ Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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[codecov]

Codecov Report

Merging #19547 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #19547   +/-   ##
=======================================
  Coverage   97.78%   97.78%           
=======================================
  Files         282      282           
  Lines        7640     7640           
  Branches     2109     2143   +34     
=======================================
  Hits         7471     7471           
  Misses        169      169

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