[class.copy.assign] Remove a superfluous note.

Alternatively we could have added the word "non-object"; or changed
it to say "An overloaded assignment operator must be a member function";
but it doesn't seem like it needs to be here at all.

Author: Quuxplusone

source/classes.tex

@@ -1746,11 +1746,6 @@
 one non-object parameter of type \tcode{X\&\&}, \tcode{const X\&\&}, \tcode{volatile X\&\&}, or
 \tcode{const volatile X\&\&}.
 \begin{note}
-An overloaded assignment operator must be
-declared to have only one parameter; see~\ref{over.ass}.
-\end{note}
-{}
-\begin{note}
 More than one form of move assignment operator can be declared for a class.
 \end{note}