[except.ctor] Remove broken and unnecessary index entry.

Author: Eelis

source/exceptions.tex

@@ -346,7 +346,6 @@
 
 \rSec1[except.ctor]{Constructors and destructors}%
 \indextext{exception handling!constructors and destructors}%
-\indextext{stack unwinding!see exception handling, constructors and destructors}%
 \indextext{constructor!exception~handling|see{exception handling, constructors and destructors}}%
 \indextext{destructor!exception~handling|see{exception handling, constructors and destructors}}