Renamed unset back to clear because unset is a reserved word which is the whole reason I didn't name it unset in the first place

core/lib/Drupal/Core/Config/DrupalConfig.php

@@ -170,9 +170,8 @@ class DrupalConfig {
    *
    * @param $key
    *   @todo
-   *
    */
-  public function unset($key) {
+  public function clear($key) {
     $parts = explode('.', $key);
     if (count($parts) == 1) {
       unset($this->data[$key]);

core/modules/image/image.module

@@ -1017,7 +1017,7 @@ function image_effect_save($style_name, $effect) {
  */
 function image_effect_delete($style_name, $effect) {
   $config = config('image.styles.' . $style_name);
-  $config->unset('effects.' . $effect['ieid']);
+  $config->clear('effects.' . $effect['ieid']);
   $config->save();
   $style = image_style_load($style_name);
   image_style_flush($style);