Clean up "replace" section

Author: nicolas-grekas

composer.json

@@ -61,13 +61,9 @@
         }
     },
     "replace": {
-        "paragonie/random_compat": "2.*",
         "symfony/polyfill-ctype": "*",
         "symfony/polyfill-iconv": "*",
-        "symfony/polyfill-php72": "*",
-        "symfony/polyfill-php71": "*",
-        "symfony/polyfill-php70": "*",
-        "symfony/polyfill-php56": "*"
+        "symfony/polyfill-php72": "*"
     },
     "scripts": {
         "auto-scripts": [