fix: remove extra 'use client' directive

[Kinbaum]

When using Next.js and SWC plugin coverage instrumentation, you will get this error due to the duplication of the use client directive:

Error: 
  × The "use client" directive must be placed before other expressions. Move it to the top of the file to resolve this issue.
   ╭─[/node_modules/.pnpm/vaul@0.9.0_@types+react-dom@18.2.17_@types+react@18.2.43_react-dom@18.2.0_react@18.2.0/node_modules/vaul/dist/index.mjs:1:1]
 1 │ "use client"
 2 │ "use client";import * as L from "@radix-ui/react-dialog";

Since you've already got this included in the index, there's no need for this config option.
Removing the banner resolves the issue with the plugin.

[vercel]

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