use MOTD_BANNED_TAGS in motd editor view

app/templates/mod/motd.html

@@ -9,7 +9,7 @@
     <label for="title">Title</label>
     <input name="title" id="title" type="text" required autocomplete="off" placeholder="Required" value="{{ current.title }}"><br>
     <label for="body">Body</label>
-    {{ babycode_editor_component('body', ta_placeholder='MOTD body (required)', banned_tags=['img', 'spoiler', '@mention'], prefill=current.body_original_markup) }}
+    {{ babycode_editor_component('body', ta_placeholder='MOTD body (required)', banned_tags=MOTD_BANNED_TAGS, prefill=current.body_original_markup) }}
     <input type="submit" value="Save">
     <input class="critical" type="submit" formaction="{{ url_for('mod.motd_delete') }}" value="Delete MOTD" formnovalidate {{"disabled" if not current else ""}}>
   </form>