DEP Don't include vendor-plugin as an explicit dependency (#3043)

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

composer.json

@@ -25,8 +25,7 @@
         "silverstripe/reports": "^6",
         "silverstripe/siteconfig": "^6",
         "silverstripe/versioned": "^3",
-        "silverstripe/versioned-admin": "^3",
-        "silverstripe/vendor-plugin": "^2"
+        "silverstripe/versioned-admin": "^3"
     },
     "require-dev": {
         "phpunit/phpunit": "^11.3",