Remove link tag around constant tag

Constant tags now support linking, so this is useless

Author: Girgias

language-snippets.ent

@@ -4370,7 +4370,7 @@ local: {
    <para>
     If omitted, <constant>FILTER_DEFAULT</constant> will be used, which is
     equivalent to
-    <link linkend="filter.filters.sanitize"><constant>FILTER_UNSAFE_RAW</constant></link>.
+    <constant>FILTER_UNSAFE_RAW</constant>.
     This will result in no filtering taking place by default.
    </para>
   </listitem>