[meta] Convert non-controller forms to FormInterface

#1971384: [META] Convert page callbacks to controllers covers all controller-based forms, but there are several others that need converting.

core/includes/install.core.inc:1315:
    $form = drupal_get_form('install_select_profile_form', $install_state);

core/includes/install.core.inc:1558:
    $elements = drupal_get_form('install_select_language_form', count($files) > 1 ? $files : array());

core/modules/comment/comment.admin.inc:30:
    return drupal_get_form('comment_admin_overview', $type);

core/modules/dblog/lib/Drupal/dblog/Controller/DbLogController.php:119:
    $build['dblog_filter_form'] = drupal_get_form('dblog_filter_form');

core/modules/dblog/lib/Drupal/dblog/Controller/DbLogController.php:120:
    $build['dblog_clear_log_form'] = drupal_get_form('dblog_clear_log_form');

core/modules/language/language.admin.inc:345:
    return drupal_get_form('language_content_settings_form', language_entity_supported());

core/modules/path/path.admin.inc:20:
    $build['path_admin_filter_form'] = drupal_get_form('path_admin_filter_form', $keys);

core/modules/path/path.admin.inc:117:
    $output = drupal_get_form('path_admin_form', $path);

core/modules/path/path.admin.inc:120:
    $output = drupal_get_form('path_admin_form');

core/modules/search/search.pages.inc:71:
    $build['search_form'] = drupal_get_form('search_form', $plugin);

core/modules/search/tests/modules/search_embedded_form/search_embedded_form.module:56:
    $form = drupal_get_form('search_embedded_form_form');

core/modules/system/system.admin.inc:149:
    $build['admin_form'] = drupal_get_form('system_themes_admin_form', $admin_theme_options);

core/modules/system/tests/modules/ajax_test/ajax_test.module:100:
    $build['form'] = drupal_get_form('ajax_test_dialog_form');

core/modules/system/tests/modules/form_test/form_test.module:2066:
    'form1' => drupal_get_form('form_test_html_id'),

core/modules/system/tests/modules/form_test/form_test.module:2067:
    'form2' => drupal_get_form('form_test_html_id'),

core/update.php:56:
    $elements = drupal_get_form('update_script_selection_form');