Remove mysqlnd plugin manuals

Hi PHP folks,

I have browsed through PHP manual looking at the mysqlnd plugins. They
contain some cool ideas and don't really harm anyone but they not are very
helpful anymore. I assume most PHP users aren't even aware of these
plugins. They seem to be only dead manual stubs for the most part.

mysqlnd_ms - Maintained by sergiotabanelli on GitHub
https://github.com/sergiotabanelli/mysqlnd_ms Original:
https://pecl.php.net/package/mysqlnd_ms
mysqlnd_qc - PECL page says it is not maintained for the past 7 years. I
think Sergio tried to fork it but I don't know what is the status.
https://pecl.php.net/package/mysqlnd_qc
mysqlnd_uh - It was never released. https://pecl.php.net/package/mysqlnd_uh
mysqlnd_mux - It was never developed. Only PoC is available.
mysqlnd_memcache - Released in 2012 but seems to have been abandoned since
then. https://pecl.php.net/package/mysqlnd_memcache

Most of these plugins are unlikely to work with PHP 8 or even PHP 7 for
that matter. I propose we remove them from the official PHP manual. If
anyone ever takes them over, they would need to update the documentation
anyway. Regarding mysqlnd_ms Sergio seems to have his own documentation on
GH https://github.com/sergiotabanelli/mysqlnd_ms/blob/master/docs/BOOK.md
which is different from the original plugin documented on php.net.

If there are any reasons to keep on maintaining these pages in the official
docs please let me know.

Kind Regards,
Kamil Tekiela