MC-16957: PHP 7.3 Cleanup Composer Repositories and Versions

Author: ffalkone

composer.json

@@ -36,7 +36,7 @@
         "colinmollenhour/php-redis-session-abstract": "~1.4.0",
         "composer/composer": "^1.6",
         "elasticsearch/elasticsearch": "~2.0|~5.1|~6.1",
-        "magento/composer": "dev-master",
+        "magento/composer": "~1.5.0",
         "magento/magento-composer-installer": ">=0.1.11",
         "magento/zendframework1": "~1.14.2",
         "monolog/monolog": "^1.17",
@@ -334,11 +334,5 @@
             "Magento\\TestFramework\\Utility\\": "dev/tests/static/framework/Magento/TestFramework/Utility/"
         }
     },
-    "repositories": [
-        {
-            "type": "vcs",
-            "url": "https://github.com/magento/composer"
-        }
-    ],
     "prefer-stable": true
 }