Remove merge plugin config

No longer needed, see previous commit

composer.json

@@ -71,15 +71,5 @@
         "preferred-install": "dist"
     },
     "minimum-stability": "dev",
-    "prefer-stable": true,
-    "extra": {
-        "merge-plugin": {
-            "include": [
-                "plugins/*/*/composer.json"
-            ],
-            "recurse": true,
-            "replace": false,
-            "merge-dev": false
-        }
-    }
+    "prefer-stable": true
 }