doc: remove outdated footnote (Python 2 --> 3 for V8 tests)

Various Python 3 compatibility fixes were made in upstream V8,
and they have even dropped Python 2 compatibility in various scripts.

depot_tools, which bootstraps the V8 build, is also moving to Python 3.

As of Node v18.0.0-ish, this footnote is no-longer accurate.

(Running `make test-v8` no-longer requires Python 2,
and it won't work anymore if you don't have a copy of Python 3.)

PR-URL: https://github.com/nodejs/node/pull/43105
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Jackson Tian <shyvo1987@gmail.com>

doc/contributing/maintaining-V8.md

@@ -407,10 +407,8 @@ This would require some tooling to:
 [^1]: Node.js 0.12 and older are intentionally omitted from this document
     as their support has ended.
 
-[^2]: The V8 tests still require Python 2. To run these tests locally, you can
-    run `PYTHON2 ./configure.py` before running `make test-v8`, in the root
-    of this repository. On macOS, this also requires a full Xcode install,
-    not just the "command line tools" for Xcode.
+[^2]: On macOS, the V8 tests require a full Xcode install, not just the "command
+    line tools" for Xcode.
 
 [ChromiumReleaseCalendar]: https://www.chromium.org/developers/calendar
 [Node.js CI]: https://ci.nodejs.org/job/node-test-pull-request/