Remove spurious "()" from the __str__() description.

Doc/lib/emailmessage.tex

@@ -38,7 +38,7 @@ Return the entire formatted message as a string.  Optional
 envelope header; it defaults to 0.
 \end{methoddesc}
 
-\begin{methoddesc}[Message]{__str__()}{}
+\begin{methoddesc}[Message]{__str__}{}
 Equivalent to \method{aMessage.as_string(unixfrom=1)}.
 \end{methoddesc}