Deleted plugin, but blog still shows "active and ready to add widgets" message

Decided a quiz isn’t right for my blog after all, so I deleted the Slick Quiz plugin, but the following message won’t go away from my header:

“Quiz Box / This panel is active and ready for you to add some widgets via the WP Admin”

The plugin was installed on a LAMP installation, so I can’t give a link that shows the problem message.

Here is what I had in functions.php:`//quiz in header
if (function_exists(‘register_sidebar’)) {

register_sidebar(array(
‘name’ => ‘quiz-box’,
‘id’ => ‘quiz-box’,
‘description’ => ‘Widgetized area in header for a quiz app’,
‘before_widget’ => ‘<div id=”%1$s” class=”widget %2$s”>’,
‘after_widget’ => ‘</div>’,
‘before_title’ => ‘<h4>’,
‘after_title’ => ‘</h4>’
));
}

//text-box in header
if (function_exists(‘register_sidebar’)) {

register_sidebar(array(
‘name’ => ‘text-box’,
‘id’ => ‘text-box’,
‘description’ => ‘Widgetized area in header for a text box’,
‘before_widget’ => ‘<div id=”%1$s” class=”widget %2$s”>’,
‘after_widget’ => ‘</div>’,
‘before_title’ => ‘<h4>’,
‘after_title’ => ‘</h4>’
));
}
`
Deleting the above code removed the widget from the admin area, but the message persisted. Because the plugin was registered from a child theme, I tried making a new child, minus the above code, but that didn’t work.

How can I de-register the plugin? Thanks.

https://www.ads-software.com/plugins/slickquiz/