[depr.template.template] Add cross-ref to core language

Add a cross reference to the core language paragraph that
contains the deprecation notice, [temp.names] (p6).

Author: AlisdairM

source/future.tex

@@ -202,7 +202,7 @@
 \pnum
 The use of the keyword \keyword{template}
 before the qualified name of a class or alias template
-without a template argument list is deprecated.
+without a template argument list is deprecated\iref{temp.names}.
 
 \rSec1[depr.res.on.required]{Requires paragraph}