docs: recommend .end instead of .send when no body is being sent

[balazsorban44]

Fixes #33536

I was thinking to make body optional here instead:

next.js/packages/next/shared/lib/utils.ts

Line 262 in 2c6bd1e

type Send<T> = (body: T) => void

But that might result in more errors when not setting the status code correctly. So it's the easiest for us to just recommend .end() which .send() uses when there is no argument.

next.js/packages/next/server/api-utils.ts

Line 269 in c71465d

if (body === null || body === undefined) {

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Documentation / Examples

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[johannpinson]

Maybe it's need an update on the fix explanation because it's still about "send an empty body".

And can the .end() function may be documented on the API Routes page? (or not because it's a native node method).