Remove obsolete branch-alias

composer.json

@@ -4,7 +4,10 @@
     "description": "The SilverStripe Content Management System",
     "homepage": "http://silverstripe.org",
     "license": "BSD-3-Clause",
-  "keywords": ["silverstripe", "cms"],
+    "keywords": [
+        "silverstripe",
+        "cms"
+    ],
     "authors": [
         {
             "name": "SilverStripe",
@@ -30,11 +33,7 @@
         "silverstripe/serve": "dev-master",
         "se/selenium-server-standalone": "2.41.0"
     },
-  "extra": {
-    "branch-alias": {
-      "dev-master": "4.0.x-dev"
-    }
-  },
+    "extra": [],
     "scripts": {
         "lint": "phpcs -s code/ tests/"
     },