[exec.just] start is exposition-only

Author: jensmaurer

source/exec.tex

@@ -2572,7 +2572,7 @@
 namespace std::execution {
   template<>
   struct @\exposid{impls-for}@<@\exposid{decayed-typeof}@<@\exposid{just-cpo}@>> : @\exposid{default-impls}@ {
-    static constexpr auto start =
+    static constexpr auto @\exposid{start}@ =
       [](auto& state, auto& rcvr) noexcept -> void {
         auto& [...ts] = state;
         @\exposid{set-cpo}@(std::move(rcvr), std::move(ts)...);