Delete APCu Polyfill installation instructions

Removed instructions for installing APCu Polyfill for legacy APC PHP extension.

Since Symfony 6.4 uses PHP >= 8.1, it's impossible that legacy APC PHP extension to be used?

I think this shouldn't exist in Symfony 6.4 config.

Author: nacholibre

performance.rst

@@ -27,14 +27,6 @@ for maximum performance:
 
 .. _performance-install-apcu-polyfill:
 
-Install APCu Polyfill if your Server Uses APC
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If your production server still uses the legacy APC PHP extension instead of
-OPcache, install the `APCu Polyfill component`_ in your application to enable
-compatibility with `APCu PHP functions`_ and unlock support for advanced Symfony
-features, such as the APCu Cache adapter.
-
 .. _performance-enabled-locales:
 
 Restrict the Number of Locales Enabled in the Application