remove intro of begin in tuples chapter, now introduced in loop chapter

book.tex

@@ -12889,7 +12889,6 @@ translation of tuple creation.
       &\MID& \key{collect}(\itm{int})
       \MID \key{allocate}(\itm{int},\itm{type})
       \MID \key{global\_value}(\itm{name}) \\
-      &\MID& \key{begin:} ~ \Stmt^{*} ~ \Exp \\
    \Stmt &::= & \CASSIGN{\CPUT{\Exp}{\itm{int}}}{\Exp}
 \end{array}
 \]
@@ -12912,10 +12911,6 @@ where $\Type_i$ is the type of the $i$th element.
 %
 The \CGLOBALVALUE{\itm{name}} form reads the value of a global
 variable, such as \code{free\_ptr}.
-%
-\python{The \code{begin} form is an expression that executes a
-  sequence of statements and then produces the value of the expression
-  at the end.}
 
 \racket{
   The type information that you need for \CALLOCATE{$n$}{$\itm{type}$}