Method removeUnreachableBlocks

\brief Remove any unreachable basic blocks A quick check for unreachable blocks can optionally be made, otherwise the cached state is checked via hasUnreachableBlocks(), which is turned on during analysis by calling the structureReset() method. \param issuewarning is \b true if warning comments are desired \param checkexistence is \b true to force an active search for unreachable blocks \return \