Remove legacy next/link prefetch={true} warning (#68326)

## What?

Removes the warning shown in Pages Router when you use the `prefetch`
prop on `next/link`. In App Router using `prefetch={true}` opts in to
full page prefetching even when the route is dynamically rendered.

When you're working on an application that uses both pages router and
app router where the components are shared using `<Link prefetch>` would
then cause this warning in Pages Router but not in App Router.

With this change there won't be a warning in Pages Router.

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---------

Co-authored-by: JJ Kasper <[email protected]>

Author: timneutkens

packages/next/src/client/link.tsx

@@ -433,16 +433,6 @@ const Link = React.forwardRef<HTMLAnchorElement, LinkPropsReal>(
           const _: never = key
         }
       })
-
-      // This hook is in a conditional but that is ok because `process.env.NODE_ENV` never changes
-      // eslint-disable-next-line react-hooks/rules-of-hooks
-      const hasWarned = React.useRef(false)
-      if (props.prefetch && !hasWarned.current && !isAppRouter) {
-        hasWarned.current = true
-        console.warn(
-          'Next.js auto-prefetches automatically based on viewport. The prefetch attribute is no longer needed. More: https://nextjs.org/docs/messages/prefetch-true-deprecated'
-        )
-      }
     }
 
     if (process.env.NODE_ENV !== 'production') {

test/development/basic/misc.test.ts

@@ -79,43 +79,5 @@ describe.each([[''], ['/docs']])(
         expect(text).toEqual(basePath + '/%2fexample.com')
       })
     })
-
-    async function getLogs$(path) {
-      let foundLog = false
-      let browser
-      try {
-        browser = await webdriver(next.url, path)
-        const browserLogs = await browser.log()
-
-        browserLogs.forEach((log) => {
-          if (log.message.includes('Next.js auto-prefetches automatically')) {
-            foundLog = true
-          }
-        })
-      } finally {
-        if (browser) {
-          await browser.close()
-        }
-      }
-      return foundLog
-    }
-    describe('Development Logs', () => {
-      it('should warn when prefetch is true', async () => {
-        const foundLog = await getLogs$(basePath + '/development-logs')
-        expect(foundLog).toBe(true)
-      })
-      it('should not warn when prefetch is false', async () => {
-        const foundLog = await getLogs$(
-          basePath + '/development-logs/link-with-prefetch-false'
-        )
-        expect(foundLog).toBe(false)
-      })
-      it('should not warn when prefetch is not specified', async () => {
-        const foundLog = await getLogs$(
-          basePath + '/development-logs/link-with-no-prefetch'
-        )
-        expect(foundLog).toBe(false)
-      })
-    })
   }
 )