remove nested folder (#33804)

Author: Phil E. Taylor

templates/cassiopeia/templateDetails.xml

@@ -18,7 +18,6 @@
 		<filename>template_thumbnail.png</filename>
 		<folder>css</folder>
 		<folder>html</folder>
-		<folder>html/tinymce</folder>
 		<folder>images</folder>
 		<folder>js</folder>
 		<folder>scss</folder>