Removed img_check script from list

refs digitalocean/marketplace-partners#90 and digitalocean/marketplace-partners#95

- this script is breaking the build because there are some leftover logs
  from the build process that it fails on
- the logs cannot be easily removed and this issue is waiting on
  upstream resolution

ghost-image.json

@@ -56,8 +56,7 @@
         "scripts/012-configure_postfix.sh",
         "scripts/014-ufw.sh",
         "scripts/020-application_tag.sh",
-        "scripts/900-cleanup.sh",
-        "scripts/999-img_check.sh"
+        "scripts/900-cleanup.sh"
       ]
     }
   ]