remove puppetlabs/mount_core from metadata.json

The *_core modules are internal modules and vendored within Puppet AIO.
They should not be added to metadata.json.

Author: bastelfreak

metadata.json

@@ -11,10 +11,6 @@
     {
       "name": "puppetlabs/stdlib",
       "version_requirement": ">= 4.13.1 < 10.0.0"
-    },
-    {
-      "name": "puppetlabs/mount_core",
-      "version_requirement": ">= 1.0.0 < 2.0.0"
     }
   ],
   "operatingsystem_support": [