[execpol.type] Omit the class body as suggested by @jwakely

Co-authored-by: Jonathan Wakely <[email protected]>

Author: frederick-vs-ja

source/algorithms.tex

@@ -640,7 +640,7 @@
 
 \indexlibraryglobal{is_execution_policy}%
 \begin{itemdecl}
-template<class T> struct is_execution_policy : bool_constant<@\seebelow@> { };
+template<class T> struct is_execution_policy;
 \end{itemdecl}
 
 \begin{itemdescr}