[class.union.anon] Remove bogus index entry that was causing excess

vertical whitespace.

Author: zygoloid

source/classes.tex

@@ -3295,7 +3295,6 @@
 is declared. For the purpose of name lookup, after the anonymous union
 definition, the members of the anonymous union are considered to have
 been defined in the scope in which the anonymous union is declared.
-\indextext{initialization!\idxcode{union}}%
 \begin{example}
 \begin{codeblock}
 void f() {