Remove two remaining {\tt ...} constructs.

Doc/ref/ref5.tex

@@ -691,7 +691,7 @@ C, \code{!=} is preferred; where \code{!=} is mentioned below
 \code{<>} is also acceptable.  At some point in the (far) future,
 \code{<>} may become obsolete.
 
-The operators {\tt "<", ">", "==", ">=", "<="}, and {\tt "!="} compare
+The operators \texttt{"<", ">", "==", ">=", "<="}, and \texttt{"!="} compare
 the values of two objects.  The objects needn't have the same type.
 If both are numbers, they are coverted to a common type.  Otherwise,
 objects of different types \emph{always} compare unequal, and are