Getting Drupal 8 project to build from composer.json instead of project.make.yml file

composer.json

{
    "name": "my/project",
    "description": "My platform.sh Drupal 8 / Composer project",
    "type": "project",
    "license": "GPL-2.0+",
    "authors": [
        {
            "name": "",
            "role": ""
        }
    ],
    "repositories": [
        {
            "type": "composer",
            "url": "https://packagist.drupal-composer.org"
        },
        {
            "type": "vcs",
            "url": "https://github.com/steveoliver/user_import.git"
        },
        {
            "type": "vcs",
            "url": "https://github.com/steveoliver/media_entity_embeddable_video.git"
        },
        {
            "type": "vcs",
            "url": "https://github.com/steveoliver/media_entity_image.git"
        }
    ],
    "require": {
        "composer/installers": "^1.0.20",
        "cweagans/composer-patches": "~1.0",
        "drupal/admin_toolbar": "8.1.11",
        "drupal/bootstrap": "8.3.*",
        "drupal/console": "~0.10",
        "drupal/core": "8.0.*",
        "drupal/deploy": "*",
        "drupal/devel": "8.*",
        "drupal/field_collection": "*",
        "drupal/inline_entity_form": "*",
        "drupal/key_value": "*",
        "drupal/media_entity": "8.1.*",
        "drupal/media_entity_embeddable_video": "8.*",
        "drupal/media_entity_image": "dev-add-composer-json",
        "drupal/multiversion": "*",
        "drupal/relaxed": "*",
        "drupal/restui": "8.1.11",
        "drupal/user_import": "*",
        "drush/drush": "~8.0"
    },
    "require-dev": {
        "behat/mink": "~1.6",
        "behat/mink-goutte-driver": "~1.2",
        "jcalderonzumba/gastonjs": "^1.1@dev",
        "jcalderonzumba/mink-phantomjs-driver": "dev-master#10d7c48c9a4129463052321b52450d98983c4332",
        "mikey179/vfsStream": "~1.2",
        "phpunit/phpunit": "~4.8",
        "symfony/css-selector": "2.7.*"
    },
    "conflict": {
        "drupal/drupal": "*"
    },
    "minimum-stability": "dev",
    "prefer-stable": true,
    "scripts": {
        "post-install-cmd": "sh ./scripts/composer/post-install.sh"
    },
    "extra": {
        "installer-paths": {
            "www/core": ["type:drupal-core"],
            "www/modules/contrib/{$name}": ["type:drupal-module"],
            "www/profiles/contrib/{$name}": ["type:drupal-profile"],
            "www/themes/contrib/{$name}": ["type:drupal-theme"],
            "drush/contrib/{$name}": ["type:drupal-drush"]
        }
    }
}