Remove extras from composer.json.

[ci skip]

composer.json

@@ -27,10 +27,5 @@
     },
     "autoload": {
         "psr-4": {"Predis\\": "src/"}
-    },
-    "extra": {
-        "branch-alias": {
-            "dev-master": "1.0-dev"
-        }
     }
 }