Remove mention of deprecated "api_platform.metadata_cache" parameter

Author: teohhanhui

core/performance.md

@@ -140,16 +140,6 @@ API Platform internally uses a [PSR-6](http://www.php-fig.org/psr/psr-6/) cache.
 Best performance is achieved using [APCu](https://github.com/krakjoe/apcu). Be sure to have the APCu extension installed
 on your production server. API Platform will automatically use it.
 
-This parameter can be changed by changing the value of `api_platform.metadata_cache`:
-
-```yaml
-# api/config/config.yaml
-
-parameters:
-    # Enable the metadata cache to speedup the builds
-    api_platform.metadata_cache: true
-```
-
 ## Using PPM (PHP-PM)
 
 Response time of the API can be improved up to 15x by using [PHP Process Manager](https://github.com/php-pm/php-pm). If