fix: remove dependency on slevomat/coding-standard

The coding standard package depends on it

Author: williamdes

composer.json

@@ -52,7 +52,6 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^7 || ^8 || ^9",
-        "slevomat/coding-standard": "^6.0",
         "phpstan/phpstan": "^0.12",
         "wdes/coding-standard": "^3"
     }