remove env import from next.config.mjs

Author: charleslien

web/next.config.mjs

@@ -1,6 +1,5 @@
 import createMDX from '@next/mdx'
 import { withContentlayer } from 'next-contentlayer'
-import { env } from '@codebuff/internal/env'
 
 const withMDX = createMDX({
   extension: /\.mdx?$/,