remove pre-configured platform PHP version

Author: xabbuh

src/Symfony/Installer/NewCommand.php

@@ -350,6 +350,18 @@ protected function updateComposerJson()
             unset($contents['description']);
         }
 
+        if (isset($contents['config']['platform']['php'])) {
+            unset($contents['config']['platform']['php']);
+
+            if (empty($contents['config']['platform'])) {
+                unset($contents['config']['platform']);
+            }
+
+            if (empty($contents['config'])) {
+                unset($contents['config']);
+            }
+        }
+
         if (isset($contents['extra']['branch-alias'])) {
             unset($contents['extra']['branch-alias']);
         }