[ticket/16449] Rename template variable PRE to S_PRE_STEP

PHPBB3-16449

phpBB/adm/style/acp_ext_delete_data.html

@@ -13,7 +13,7 @@
 			<p>{{ MIGRATOR_ERROR }}</p>
 			<p><a href="{{ U_RETURN }}">{{ lang('RETURN_TO_EXTENSION_LIST') }}</a></p>
 		</div>
-	{% elseif PRE %}
+	{% elseif S_PRE_STEP %}
 		<div class="errorbox">
 			<p>{{ CONFIRM_MESSAGE }}</p>
 		</div>