docs: Add note about remove of the `swcMinify` flag (#73281)
### What?
Docs update.
As noted in, https://github.com/vercel/next.js/issues/73267, swcMinify,
is still listed in the documentation, though the flag has been removed.
### Why?
The flag has been removed.
### How?
Add a note, for reference, that the flag has been removed, rather than
dropping the entire Minification section.
I wonder, though, what is the recommended way to opt-out, and into
Terser again, should you find an issue with SWC's minification?
Hi-jacking the minifier in the Webpack config object?
Fixes #73267
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Co-authored-by: Delba de Oliveira <32464864+delbaoliveira@users.noreply.github.com>
