[class] Remove misplaced index entries (#2084)

Author: jensmaurer

source/classes.tex

@@ -117,12 +117,8 @@
 \end{note}
 
 \pnum
-\indextext{\idxcode{struct}!\tcode{class} versus}%
-\indextext{structure}%
-\indextext{\idxcode{union}!\tcode{class} versus}%
 A \defn{union} is a class defined with the \grammarterm{class-key}
 \tcode{union};
-\indextext{access control!\idxcode{union} default member}%
 it holds at most one data member at a time\iref{class.union}.
 \begin{note}
 Aggregates of class type are described in~\ref{dcl.init.aggr}.