[class.copy.assign] Fix phrasing in note to avoid 'could'. (#4418)

Author: jensmaurer

source/classes.tex

@@ -1870,11 +1870,13 @@
 a base class copy/move assignment operator is always hidden
 by the corresponding assignment operator of a derived class\iref{over.ass}.
 \begin{note}
-A \grammarterm{using-declaration} that names an assignment operator
-with a parameter type that could be that of a
-copy/move assignment operator for a
-derived class does not suppress the implicit declaration of the derived class
-operator\iref{namespace.udecl}.
+A \grammarterm{using-declaration} in a derived class \tcode{C}
+that names an assignment operator from a base class
+never suppresses the implicit declaration of
+an assignment operator of \tcode{C},
+even if the base class assignment operator would be
+a copy or move assignment operator
+if declared as a member of \tcode{C}.
 \end{note}
 
 \pnum