[exec.snd.expos] Remove itemdecl "write-env".

An omission in the application of P3284R4.

Author: tkoeppe

source/exec.tex

@@ -2085,57 +2085,6 @@
 where \tcode{\placeholder{unspecified-exception}} is
 a type derived from \tcode{exception}.
 
-\begin{itemdecl}
-template<@\libconcept{sender}@ Sndr, @\exposconcept{queryable}@ Env>
-  constexpr auto @\exposid{write-env}@(Sndr&& sndr, Env&& env);     // \expos
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\exposid{write-env} is an exposition-only sender adaptor that,
-when connected with a receiver \tcode{rcvr},
-connects the adapted sender with a receiver
-whose execution environment is the result of
-joining the \exposconcept{queryable} argument \tcode{env}
-to the result of \tcode{get_env(rcvr)}.
-
-\pnum
-Let \exposid{write-env-t} be an exposition-only empty class type.
-
-\pnum
-\returns
-\begin{codeblock}
-@\exposid{make-sender}@(@\exposid{write-env-t}@(), std::forward<Env>(env), std::forward<Sndr>(sndr))
-\end{codeblock}
-
-\pnum
-\remarks
-The exposition-only class template \exposid{impls-for}\iref{exec.snd.general}
-is specialized for \exposid{write-env-t} as follows:
-\begin{codeblock}
-template<>
-struct @\exposid{impls-for}@<@\exposid{write-env-t}@> : @\exposid{default-impls}@ {
-  static constexpr auto @\exposid{get-env}@ =
-    [](auto, const auto& state, const auto& rcvr) noexcept {
-      return @\seebelow@;
-    };
-};
-\end{codeblock}
-Invocation of
-\tcode{\exposid{impls-for}<\exposid{write-env-t}>::\exposid{get-env}}
-returns an object \tcode{e} such that
-\begin{itemize}
-\item
-\tcode{decltype(e)} models \exposconcept{queryable} and
-\item
-given a query object \tcode{q},
-the expression \tcode{e.query(q)} is expression-equivalent
-to \tcode{state.query(q)} if that expression is valid,
-otherwise, \tcode{e.query(q)} is expression-equivalent
-to \tcode{get_env(rcvr).que\-ry(q)}.
-\end{itemize}
-\end{itemdescr}
-
 \begin{itemdecl}
 template<class T, class Context>
   decltype(auto) @\exposid{allocator-aware-forward}@(T&& obj, Context&& context);       // \expos