[FIX](Realpath)

As PHP 7.2 provide a default value of 4096k (as seen https://github.com/php/php-src/blob/php-7.2.0RC6/UPGRADING#L357), the line about this improvement can be deleted.

Author: Guikingone

performance.rst

@@ -79,15 +79,11 @@ real and absolute file system paths. This increases the performance for
 applications like Symfony that open many PHP files, especially on Windows
 systems.
 
-By default, PHP sets a ``realpath_cache_size`` of ``16K`` which is too low for
-Symfony. Consider updating this value at least to ``4096K``. In addition, cached
-paths are only stored for ``120`` seconds by default. Consider updating this
-value too using the ``realpath_cache_ttl`` option:
+By default, cached paths are only stored for ``120`` seconds by default, consider updating this value using the ``realpath_cache_ttl`` option:
 
 .. code-block:: ini
 
     ; php.ini
-    realpath_cache_size=4096K
     realpath_cache_ttl=600
 
 .. index::