textareas should be treated like text inputs

wagtail/wagtailadmin/static/wagtailadmin/scss/layouts/page-editor.scss

@@ -266,7 +266,8 @@
             padding-bottom:1.2em;
         }
 
-        .struct-block .widget-text_input > label{
+        .struct-block .widget-text_input > label,
+        .struct-block .widget-textarea > label{
             display:none;
         }