make sure classes are stripped when styles are set without specifying classes (#5269)

Author: stuartromanek

.changeset/hungry-animals-joke.md

@@ -0,0 +1,5 @@
+---
+"apostrophe": patch
+---
+
+if no class provided for a rt style set it to null to ensure removal

packages/apostrophe/modules/@apostrophecms/rich-text-widget/ui/apos/components/AposRichTextWidgetEditor.vue

@@ -670,6 +670,8 @@ export default {
         // Handle custom attributes
         if (style.class) {
           style.options.class = style.class;
+        } else {
+          style.options.class = null;
         }
 
         if (!style.type) {