Remove leftover from backporting that breaks compilation of xml2

The tuplestore in xpath_table() is created with random access even
though it might not require it, the scaffolding for dealing with
relaxing this (commit 05bba3d1) came
the in 8.4 cycle and is yet to be merged. For now drop down to always
requesting random access awaiting the merge of the 8.4 patches.

contrib/xml2/xpath.c

@@ -690,9 +690,7 @@ xpath_table(PG_FUNCTION_ARGS)
 	 * Create the tuplestore - work_mem is the max in-memory size before a
 	 * file is created on disk to hold it.
 	 */
-	tupstore =
-		tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
-							  false, work_mem);
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
 
 	MemoryContextSwitchTo(oldcontext);