Fix Explicate control in Chapter 5.

There are leftovers of C_Clos.

book.tex

@@ -10502,10 +10502,10 @@ generate better code by taking this fact into account.
 
 The output language of \code{explicate\_control} is \LangCLoop{}
 (Figure~\ref{fig:c7-syntax}), which is nearly identical to
-\LangCLam{}. The only syntactic difference is that \code{Call} and
-\code{read} may also appear as statements.  The most significant
-difference between \LangCLam{} and \LangCLoop{} is that the
-control-flow graphs of the later may contain cycles.
+\LangCIf{}. The only syntactic difference is that
+\code{read} may also appear as a statement.  The most significant
+difference between programs in \LangCIf{} and programs in \LangCLoop{}
+is that the control-flow graphs of the later may contain cycles.
 
 \begin{figure}[tp]
 \fbox{