[String] Move Inflector's polyfill-ctype dependency to String.

Author: derrabus

composer.json

@@ -25,7 +25,6 @@
     "require": {
         "php": "^7.2.5",
         "symfony/deprecation-contracts": "^2.1",
-        "symfony/polyfill-ctype": "~1.8",
         "symfony/string": "^5.1"
     },
     "autoload": {