Remove unused class selector.

This is an artefact and should have been removed when we removed the rich text survey component.

GitOrigin-RevId: cdda625b02328b8c300a91178733321ecfcd7290

services/web/frontend/stylesheets/app/editor.less

@@ -768,8 +768,7 @@ CodeMirror
   z-index: @zindex-popover;
 }
 
-.compile-time-warning,
-.rich-text-survey-warning {
+.compile-time-warning {
   padding: @padding-sm;
   background-color: @ol-green;
   width: 420px;