MNT Remove obsolete branch-alias

composer.json

@@ -3,7 +3,12 @@
     "description": "Provides an API for building environment tests",
     "license": "BSD-3-Clause",
     "type": "silverstripe-vendormodule",
-    "keywords": ["silverstripe", "testing", "environment", "check"],
+    "keywords": [
+        "silverstripe",
+        "testing",
+        "environment",
+        "check"
+    ],
     "authors": [
         {
             "name": "Will Rossiter",
@@ -23,11 +28,7 @@
         "sminnee/phpunit": "^5.7",
         "squizlabs/php_codesniffer": "^3.0"
     },
-    "extra": {
-        "branch-alias": {
-            "dev-master": "2.2.x-dev"
-        }
-    },
+    "extra": [],
     "autoload": {
         "psr-4": {
             "SilverStripe\\EnvironmentCheck\\": "src/",
@@ -36,4 +37,4 @@
     },
     "minimum-stability": "dev",
     "prefer-stable": true
-}
+}