build: remove mips support

Upstream V8 is dropping support for mips/mipsel/mips64/mips64el.
This commit removes the build flags from the configure script
and some loose ends from the documentation.

PR-URL: https://github.com/nodejs/node/pull/26192
Fixes: https://github.com/nodejs/node/issues/26179


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>