fix(vercel): remove requestContext

[yusukebe]

Fixes #3548

The requestContext, which is used in the second argument of the handler, is no longer needed. Because the current version of Next.js passes only the values of params. But, you can get the params value from c.req.param().

Ref: https://nextjs.org/docs/app/api-reference/file-conventions/route#context-optional
Ref: https://nextjs.org/docs/app/building-your-application/routing/dynamic-routes#typescript

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.29%. Comparing base (631c001) to head (c7022aa).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3549   +/-   ##
=======================================
  Coverage   94.29%   94.29%           
=======================================
  Files         157      157           
  Lines        9499     9499           
  Branches     2885     2852   -33     
=======================================
  Hits         8957     8957           
  Misses        542      542           

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