LazUtils: Remove test version of overridden InsertItem from TDictionaryStringList. It is called from FPC > 2.7.1. Solves issue #24964 although not the way it suggested.

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42649 4005530d-fff6-0310-9dd1-cebe43e6787f