LWG4447 Remove unnecessary sizeof…(Env) > 1 condition

Fixes US 206-325 (C++26 CD).

Author: burblebee

source/exec.tex

@@ -791,8 +791,7 @@
 For type \tcode{Sndr} and pack of types \tcode{Env},
 let \tcode{CS} be \tcode{completion_signatures_of_t<Sndr, Env...>}.
 Then \tcode{\exposid{single-sender-value-type}<Sndr, Env...>} is ill-formed
-if \tcode{CS} is ill-formed or
-if \tcode{sizeof...(Env) > 1} is \tcode{true};
+if \tcode{CS} is ill-formed;
 otherwise, it is an alias for:
 \begin{itemize}
 \item