[class.conv.fct] Remove line incorrectly stating that "operator auto" is well-formed

Author: eisenwave

source/classes.tex

@@ -2712,7 +2712,6 @@
 \begin{example}
 \begin{codeblock}
 struct S {
-  operator auto() const { return 10; }      // OK
   template<class T>
   operator auto() const { return 1.2; }     // error: conversion function template
 };