Turbopack: Remove beta warning (#82797)

Feedback from @feedthejim:

- It's scarier than it needs to be, beta builds should be fine for most users.
- This is opt-in, so users probably aren't going to use it by accident.
- We don't tend to do this level of warning for other feature flags.

Author: bgw

packages/next/src/build/index.ts

@@ -4022,10 +4022,6 @@ export default async function build(
     // Ensure we wait for lockfile patching if present
     await lockfilePatchPromise.cur
 
-    if (isTurbopack && !process.env.__NEXT_TEST_MODE) {
-      warnAboutTurbopackBuilds()
-    }
-
     // Ensure all traces are flushed before finishing the command
     await flushAllTraces()
     teardownTraceSubscriber()
@@ -4050,14 +4046,6 @@ function errorFromUnsupportedSegmentConfig(): never {
   process.exit(1)
 }
 
-function warnAboutTurbopackBuilds() {
-  Log.ready(
-    `Turbopack builds are ${bold('beta')}.\n\n` +
-      '   Please see our docs https://nextjs.org/docs/app/api-reference/turbopack for information on known differences with webpack builds.\n\n' +
-      '   Provide feedback for Turbopack builds at https://github.com/vercel/next.js/discussions/77721'
-  )
-}
-
 function getBundlerForTelemetry(isTurbopack: boolean) {
   if (isTurbopack) {
     return 'turbopack'