DEP Don't include vendor-plugin as an explicit dependency (#916)

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

composer.json

@@ -31,7 +31,6 @@
     },
     "require": {
         "php": "^8.3",
-        "silverstripe/vendor-plugin": "^2",
         "silverstripe/framework": "^6",
         "silverstripe/admin": "^3",
         "silverstripe/versioned": "^3",
@@ -70,4 +69,4 @@
             "silverstripe/vendor-plugin": true
         }
     }
-}
+}