…ed as of 3.0.0 by @ImRodry"

This reverts commit 4d9b113.

node-fetch@3 makes two major changes: they started shipping TS types
with the package, and they switched it to being an ESM-only module. The
latter means that apps which aren't built in a way that supports ESM (or
other npm modules depending on `node-fetch` which don't want to break
their non-ESM users) need to continue using v2. In fact, the README for
`node-fetch` explicitly states

> If you cannot switch to ESM, please use v2 which remains compatible
> with CommonJS. Critical bug fixes will continue to be published for
> v2.

Stats on npmjs.com show that v2 has 43 times more downloads in the past
7 days than v3.

I applaud node-fetch's forward-thinking approach to ESM, and am not here
to tell them that their choice for v3 is wrong. But practically speaking,
v2 is still heavily used and many projects will not be able to upgrade
to v3 without breaking their own backwards compatibility promises.
So it makes sense to continue to maintain v2-specific node-fetch types
(especially as there are specific issues with the published types,
as the next commit in this PR shows).

v2.6 is the current (and presumably final) minor release of v2.
Apparently these types already included at least one v2.6 feature
(`agent` as a function). So, updating the version as suggested at-rule
DefinitelyTyped#55533 (comment)

The `agent` option is (after checking to see if it's a function, and if
so replacing itself with the return value of calling it) passed directly
to `http.request` (or `https.request`) so we should be able to pass any
type supported there. Notably, `agent: false` is distinct from `agent:
undefined`.

A PR making essentially the same change was merged upstream (the
upstream repo maintains their own types for v3 but not for v2):
node-fetch/node-fetch#1502

Co-authored-by: Nicolas Rodriguez <programnicolas@gmail.com>

Co-authored-by: Niklas Lindgren <nikc@iki.fi>

Co-authored-by: Piotr Błażejewicz (Peter Blazejewicz) <peterblazejewicz@users.noreply.github.com>