LWG2940 result_of specification also needs a little cleanup

Author: Dawn Perchik

source/future.tex

@@ -2111,7 +2111,8 @@
 
 \pnum
 The behavior of a program that adds specializations for
-\tcode{is_literal_type} or \tcode{is_literal_type_v} is undefined.
+any of the templates defined in this subclause is undefined,
+unless explicitly permitted by the specification of the corresponding template.
 
 \rSec1[depr.iterator.primitives]{Deprecated iterator primitives}