Don't use text escape with \textbf inside lstlisting

The use of boldface was inconsistent with the rest of the listing anyway.

chapters/stream.tex

@@ -331,7 +331,7 @@ \section{Stream Operator inStream and Connection Equations}\doublelabel{stream-o
 \end{lstlisting}
 More sophisticated implementation, with smooth approximation, applied only when {all} flows are small:
 \begin{lstlisting}[language=modelica,escapechar=!,mathescape=true]
-// Define a "small number" eps (!\textbf{nominal}!(v) is the nominal value of v !--! see !\autoref{attributes-start-fixed-nominal-and-unbounded}!)
+// Define a "small number" eps (nominal(v) is the nominal value of v -- see !\autoref{attributes-start-fixed-nominal-and-unbounded}!)
 eps := relativeTolerance*min(nominal($m_j$.c.m_flow));
 
 // Define a smooth curve, such that  alpha($s_i>=eps$)=1 and alpha($s_i<0$)=0