[meta.type.synop, meta.const.eval] Rewrite declarations using auto

See #4822 for the general policy on when to use abbreviated function
template syntax.

Author: burblebee

source/meta.tex

@@ -583,8 +583,7 @@
 
   // \ref{meta.const.eval}, constant evaluation context
   constexpr bool is_constant_evaluated() noexcept;
-  template<class T>
-    consteval bool is_within_lifetime(const T*) noexcept;
+  consteval bool is_within_lifetime(const auto*) noexcept;
 }
 \end{codeblock}
 
@@ -2436,8 +2435,7 @@
 
 \indexlibraryglobal{is_within_lifetime}%
 \begin{itemdecl}
-template<class T>
-  consteval bool is_within_lifetime(const T* p) noexcept;
+consteval bool is_within_lifetime(const auto* p) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}