DEP Don't include vendor-plugin as an explicit dependency (#424)

We don't directly reference it in code or config, so we can rely on silverstripe/framework having this dependency for us.

Author: GuySartorelli

composer.json

@@ -26,7 +26,6 @@
     },
     "require": {
         "php": "^8.3",
-        "silverstripe/vendor-plugin": "^2",
         "silverstripe/framework": "^6"
     },
     "require-dev": {