type(Button): remove unnecessary code

[thinkasany]

🤔 This is a ...

• TypeScript definition update

💡 Background and solution

export SizeType 已经包含了undefined 类型

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

🤖 Generated by Copilot at e81baf5

Improve code quality of button-group.tsx component. Fix import order and simplify group size context type.

🔍 Walkthrough

🤖 Generated by Copilot at e81baf5

• Simplify the type of GroupSizeContext to SizeType (link) in button-group.tsx
• Adjust the import order of modules in button-group.tsx to follow the ESLint rule import/order (link)

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[github-actions]

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (2f0c82f) 100.00% compared to head (e81baf5) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master    #43439   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          648       648           
  Lines        10968     10968           
  Branches      2978      2978           
=========================================
  Hits         10968     10968           

Impacted Files	Coverage Δ
components/button/button-group.tsx	100.00% <100.00%> (ø)

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