BMC+kInduction: Fixed a bug in the unsound havocing heuristic that made it even more unsound. Fixing it also made one of the hacks unnecessary that was used to improve the soundness of the heuristic.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13401 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c