[depr.meta.types] Remove is_literal_type index entry

This subclause doesn't mention is_literal_type; I believe the index entry is a historical artifact.

Author: CaseyCarter

source/future.tex

@@ -1470,7 +1470,6 @@
 The header \libheaderrefx{type_traits}{meta.type.synop}
 has the following addition:
 
-\indexlibraryglobal{is_literal_type}%
 \begin{codeblock}
 namespace std {
   template<class T> struct is_pod;