Orphaned advagg_mod.settings.ga_inline_to_file configuration causes schema error

Problem/Motivation

Specific settings for the Google Analytics module was removed in http://cgit.drupalcode.org/advagg/commit/advagg_mod/src/Form/SettingsFor...

However, there is still configuration being saved in \Drupal\advagg_mod\Form\SettingsForm::submitForm():

    /** @var \Drupal\Core\Config\Config $config */
    $config = $this->config('advagg_mod.settings');
    $config
      ->set('ga_inline_to_file', $form_state->getValue('ga_inline_to_file'))
      ->save();

As a result, advagg_mod.settings.yml now has a property 'advagg_mod.settings.ga_inline_to_file: 0' that is not defined in advagg_mod.schema.yml

Proposed resolution

Remove the obsolete variable ga_inline_to_file from advagg_mod.settings.

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

None.

API changes

None.

Data model changes

None.